New iPhone is coming, so when should I sell my old iPhone?

It's that time of year again when the rumors are flying about a new Apple iPhone.

Eager iPhone fans are already plotting their upgrade to the new iPhone, which is expected to be announced and launched in September. Many people who already own iPhones sell them in order to get cash to buy their next iPhones. But as the rumor mill heats up, prices typically drop. So when is the best time for an iPhone fanboy or fangirl to sell their used iPhone? I offer some advice.

Also in this Ask Maggie, I empathize with a reader who is frustrated and confused by the data plans offered by wireless operators for different devices.

The best time to sell your old iPhone is now

Dear TJ,
You are wise to start thinking about this now. I talked to Jeff Trachsel, chief marketing officer for Nextworth, a site where people can trade in their used smartphones. And he said that as the rumor mill starts churning prior to the launch of a new iPhone trade-in prices start declining. He said it's best to sell your old iPhone as soon as you can.

I checked Nextworth today and the price for a used iPhone 4S 16GB on AT&T in good condition is $263. Of course the problem is that if you trade in your phone now, you'll be without a phone until September 21, when the new iPhone is expected to go on sale.

If you have an old phone that you can use in the meantime, it could fill the void until you can get the new iPhone. If that's not an option, Nextworth offers a 21-day price guarantee. So you could lock-in a price starting on August 31, and then send your old iPhone to Nextworth when you get the new phone.

But keep in mind that the September 12 launch date and the September 21 sale date for the new iPhone are just rumors. Apple hasn't officially announced anything yet, so it's unclear if the new iPhone will really be announced on the first date and available September 21.

"If you can, the best scenario is to trade in your old iPhone sooner rather than later," Trachsel said. "But if you don't have a back-up phone you can use, then lock-in a price as close to the 21-days before the new one comes out."

Trachsel said that prices on older iPhones have already started to fall, but he said that there hasn't been a steep decline yet.

Nextworth put together a chart tracking trade-in pricing from eBay during the last iPhone launch. And what the company discovered is that in the two months leading up to the launch, as the rumor mill spun nearly out of control, the previous generations of iPhones lost about 25 percent of their value.

The iPhone 4S was launched in October 2011, and the eBay data suggests prices started declining significantly starting in August.

The same trend is likely playing out now. But Trachsel said he hasn't yet seen a big dip in pricing. Still, he said he expects that from now until the new iPhone goes on sale, there will likely be a 3 to 4 percent drop in trade-in value each week. That means there's likely to be about a 12 percent drop per month until the launch, which will result in a similar 25 percent decline in value over just a couple of months before the new iPhone is released.

Even though the prices are dropping and they will continue to drop for the next few weeks, the good news is that iPhones still hold their value better than any other smartphone on the market. Even an older iPhone 3GS in the 8GB configuration will still fetch you $80 today.

Trachsel also says to keep in mind that some retail stores will let you trade-in your old devices in person and you get paid on the spot. Nextworth powers Target's trade-in program. In fact, starting Sunday August 12, 2012 until Saturday August 18, 2012 you can bring your old iPhone to a Target and automatically get $150 for any iPhone 4, $100 for any 3GS, $50 for any 3G device. The guaranteed price on the buy-back is available only in the stores.

While it's true that you might be able to get a better price via the website, Trachsel said the benefit of the in-store trade in is that you get your cash right away. You also will get exactly the price you've been quoted. He said that sometimes when people send in phones to the Website, the prices may be revised down when it is evaluated by a Nextworth employee.

"Sometimes there is a discrepancy in the condition of the phone and what someone thinks it's worth, and what we think it's worth once we see it," he said.

I hope this advice was helpful. And good luck!

More data plan confusion

Dear Chedrcheez,
I wouldn't say that the tablet plans are priced much less than the other data plans on a carrier such as Verizon Wireless. In fact, you often get less data for a tablet than you do for a laptop. But when I looked up the pricing, what I noticed was just how confusing and inconsistent the prices are.

If you are looking for a data plan for just a single device without a smartphone sharing the data on the account, the price per gigabyte depends on which device you plan on using with your service. Verizon seems to price data for USB modems for laptops, Wi-Fi hotspots that allow multiple devices to share one cellular data connection via Wi-Fi, and tablets differently for each product.