If you wanna buy online, buy from the wireless carrier's website instead of an authorized agent's website, and pick a phone that is more recent to nearly guarantee that you'll get the phone. With an authorized agent website, there's no guarantee that the site is even legitimate and you could be taken for a ride. Some wireless carriers might have an incentive to activate it online, which you need to check with the wireless carrier you plan to go with if it's cheaper, or free to activate it online vs. in-store. I personally prefer to go to the wireless carrier's store rather than an authorized agent's store, or online as the aireless carriers' sales representative know more about the service they sell than the authorized agents do. The Wireless carrier's stores may not have the best deals over the authorized agents, but I've had better service from the wireless carrier's stores than the authorized agents. I always had to deal with attitudes and pushy sales people at authorized agents, and Radio Shack nearly screwed me up with my Verizon Wireless service the first time around that I decided to deal with Verizon Wireless themselves the second time around. I also like to deal with a sales representative to answer any questions I might have, which you may or may not get with the authorized agent, or online from the wireless carrier or the authorized agent's website.
Only you can decide what is right for you. I personally would rather pay a little more from my carrier, Verizon Wireless,going to their stores and knowing I'll get the phone I want, and know that it's in stock.