Where to unload your old iPhone for top dollar (Ask Maggie)

Apple's next iteration of the ever-popular iPhone is expected to be announced today. And eager fans are already asking questions in anticipation of buying the new device.

Where is the best place to sell old iPhones to fund the purchase of a new one? And will an AT&T version of the device that's expected to support the faster network technology HSPA+ really offer a noticeable performance boost over 3G versions of the same phone from Verizon Wireless and Sprint Nextel?

These are just two questions I tackle in this installment of the Ask Maggie column. Look for more iPhone-related questions and answers in Friday's edition of Ask Maggie.

Ask Maggie is an advice column that answers readers' wireless and broadband questions. The column now appears twice a week on CNET offering readers a double dosage of Ask Maggie's advice. If you have a question, I'd love to hear from you. Please send me an e-mail at maggie dot reardon at cbs dot com. And please put "Ask Maggie" in the subject header. You can also follow me on Facebook on my Ask Maggie page.

iPhone trade-ins

Dear Liz,
One of the best things about Apple products is that they have great resale value. Even your iPhone 3GS, which first debuted more than two years ago, can still fetch a good price today.

In fact, if your goal is to get the latest iPhone when it comes out later this month, you can probably pay for at least half of the new iPhone (assuming the subsidized cost with a carrier contract is $200) by selling your old iPhone 3GS. And if your husband sells his iPhone 4, he could easily cover the cost of a new subsidized iPhone, if he is up for a contract renewal.

So where should you start looking to sell your iPhones? You could try selling them on eBay or by placing an ad on Craigslist. But for some people hosting an auction or answering e-mails from Craigslist are hassles they'd like to avoid.

There are also dozens, if not hundreds, of Web sites dedicated to buying your used gadgets. I checked out only a handful of these Web sites on Monday to get an idea of what the going rate is for both the 16GB iPhone 3GS and the 16GB iPhone 4. My comparisons were based on the assumption that your phones are all still working and in good condition. By good condition, I mean only a few minor scratches here and there, but no major scratches and no cracked screens.

I assembled a chart, which can be seen below that gives you an idea of how much the pricing varies on these devices, as of Monday afternoon. (Keep in mind these prices were gathered the day before Apple was expected to announce its latest iPhone. So prices may change after the announcement of the new iPhone.)

A couple of things struck me as interesting when I looked at my findings. First, there is a huge difference in resale value for an iPhone 4 from AT&T versus one from Verizon Wireless. This is interesting, since the phones are exactly the same, except for the network technology that they use. Verizon's version operates on its 3G CDMA network, while AT&T's version operates on a 3G GSM network.

The difference in how much a user can get selling a used Verizon iPhone 4 and an AT&T iPhone 4 is about $150 when you compare all the sites I surveyed. The most you could get for the iPhone 4 from AT&T is $307 with eBay's Cash-in program. But Gazelle, which will offer you $191 for the AT&T iPhone 4, will only give Verizon iPhone 4 owners $154, about half of what eBay will pay for an AT&T version of the iPhone 4.

The biggest difference between prices offered for the AT&T version and the Verizon version came from Nextworth. It will pay $250 for the AT&T version of the iPhone 4, but it will offer only $165 for the Verizon version.

I suspect the price difference is due in large part to the fact that Verizon's model does not have a SIM card and is not a "world phone." This means it can only be used on Verizon's network. Meanwhile, the AT&T version is supposedly locked to AT&T, but because it's a GSM phone it has a SIM card. And it can be unlocked so that it can be used on other GSM networks around the world, including T-Mobile in the U.S. and almost any carrier network in Europe.

The other interesting thing I learned by comparing prices is that you can still get a decent amount of money for selling an iPhone 3GS, which surprises me considering the fact that the phone is more than two years old and AT&T offers a brand new iPhone 3GS for $49 with a two-year contract.

Cash for iPhones offers the most for an iPhone 3GS at $206. (Update note November 4, 2011 11:00 p.m. PT: Some consumers have complained on Twitter, to the Better Business Bureau and in online forums that Cash for iPhones is a bait-and-switch scam. They say the company promises a high price for iPhones online, and then offers much less for the products once the company receives and assesses the devices.) The Web site, Totem, offers the least for an iPhone 3GS: $114.

Of course, many of these prices could change as Apple introduces a new iPhone or perhaps multiple models of iPhones over the next couple of weeks. Even after a new model is introduced, AT&T and Verizon are likely to continue to offer the current iPhone 4 at a reduced price, just as AT&T has been selling the iPhone 3GS. At this point it's unclear what will happen to the iPhone 3GS. AT&T is likely to stop selling the device as new models come on the market.

So what should you do? If you're serious about selling either your iPhone 3GS or your husband's iPhone 4, I'd suggest that you check out these Web sites and any others that you come across and compare prices. The price each site is willing to pay tends to vary, which makes it difficult to recommend just one. So take a look at as many as you can. And keep in mind that most buy-back programs operate in a similar fashion, which means they won't pay you until they have received and tested your device to make sure it works as you've advertised. And there is a chance that once you send in your device, the company could reduce its offer. This has been the case with the site Cash For iPhones, which has been criticized by consumers for such practices.

Good luck!

Updated November 3, 2011 11:00 p.m. PT This story was updated with information about the Website Cash for iPhones, which claims to offer high trade-in prices for used iPhones. Some consumers have complained online, on Twitter, and to the Better Business Bureau that the company's practices are disingenuous because the company initially offers a higher price online and then greatly reduces the offer once the device is received and assessed.

Will an AT&T iPhone with HSPA+ really be faster?

Dear Michael,
This is a great question. In theory AT&T's HSPA+ network should be four times faster than its regular 3G network, which uses a technology called HSPA. And it should also be faster than other 3G networks, like Verizon's or Sprint's 3G networks, which use a technology called EV-DO.

Under ideal conditions, the AT&T HSPA+ network is faster than these other networks. But the problem is that the real-life conditions aren't always ideal. You mentioned network congestion as a major issue that can affect actual network speeds and that is indeed the case. But it's not just congestion on the wireless network, but there can also be congestion on what's called the backhaul network. The wireless portion of the network extends between your phone and the cell phone tower it's communicating with. The backhaul network is the network that connects the cell towers to AT&T's backbone network, which carries phone calls and data across the entire AT&T network.

Think of the wireless network like a system of roads. The actual wireless network, which uses the HSPA and HSPA+ technologies, are like the secondary roads that lead to your house. And these roads connect to a highway or the backhaul network, which then leads to even bigger interstate highways that traverse the country.

AT&T says that it has deployed HSPA+ to nearly 100 percent of its mobile broadband network. This means that it's nearly completed the upgrade of all its secondary roads. But it's still upgrading the highways or the backhaul network. Mark Siegel, an AT&T spokesman said the company expects two-thirds of its mobile broadband traffic will be carried on enhanced backhaul by the end of this year.

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This means that even if you are able to zip along all the secondary roads that have recently been widened and paved, you could still face a big traffic jam once you hit the highway. If that's the case, even though you made good time to the highway, you'll still have to sit in miles of traffic and arrive later at your destination because of the congestion. The same thing can happen in wireless networks.

So what does this mean for an AT&T customer? Well, it means that depending on where you live, the upgrade to HSPA+ may not matter all that much to you. If AT&T hasn't upgraded the backhaul network in your area, then you'll likely still face network congestion with or without HSPA+. Meanwhile, even though Verizon's 3G network may use a slower technology, if all the lanes of traffic are open on the secondary roads and the highway, you could still reach your destination much faster on that network, even though you were driving a slower car.

In fact, CNET Reviews editor Bonnie Cha said she hasn't seen much difference in network speeds when she has tested AT&T HSPA+ phones compared with other AT&T 3G phones in New York City. She also said she hasn't seen much difference between HSPA+ AT&T phones and Verizon Wireless 3G smartphones. What's more, the Verizon iPhone 4 actually outperformed the AT&T iPhone 4 in network testing in San Francisco conducted by CNET Reviews editors Kent German and Jessica Dolcourt in February.

So what does this mean for you and your iPhone 5 purchase decision? It's difficult to say for certain whether you will experience a speed boost with an iPhone that supports HSPA+. If I were you, I'd wait to see how the device fairs in actual review testing. What's more, AT&T hasn't said specifically where it has upgraded its backhaul network. And if you live in an area that is particularly prone to network congestion, my guess is that you could still see some congestion on the HSPA+ network.

Still, I suggest you talk to anyone you know with an HSPA+ phone from AT&T who lives in your area. That may be hard to do, since only a handful of devices currently use HSPA+. You could also wait to see what other say about the performance of the new iPhone with HSPA+ once it's released.

But if you can't wait, you could buy an HSPA+ phone from AT&T and see for yourself if there is a difference in speed. AT&T offers a 30-day return policy. So if you aren't satisfied, you can take it back.

And if you are considering switching to Verizon Wireless, I'd make sure that you talk to other Verizon customers you know who live and work near you to see what they think of the network's performance.

Keep in mind that Verizon's return policy is just two weeks. So if you are going to try that service, you have to make your decision quickly or you may be stuck with Verizon's service regardless of whether you like.

I hope this helps. And good luck!