you have to buy a phone from your carrier, like t-mobile uses sim cards and other services don't.

I think the answer is Yes and No. In theory, just about any cell phone will work with any cell phone provider. You often see competing services offering deals on the same model phones. However, different cellular service providers use different cell phone technologies. http://www.celusion.com/whitepapers/fdma_tdma_cdma.htm So, if you buy a cell phone meant for one provider (e.g. AT&T), it may not work on another provider's network (e.g. Verizon). Unless you have some compelling need for a particular phone, it's probably easiest to just select from the ones offered by your provider. Most providers have an extensive variety of compatible phones.

There's a little more to it than that. You cannot use any phone with any carrier because cell phones today are made with either CDMA radios or GSM radios. And a phone with a CDMA radio cannot and does not work on the GSM network and vice versa. It is very important to know that it's not about SIM cards, it's about technology. AT&T and T-Mobile use GSM technology and Verizon, Sprint, US Cellular, Alltel, MetroPCS, Cricket use CDMA. The predominant technology worldwide is GSM and in order to use a cell phone that works on a GSM network, you need a SIM card from your carrier. In the US, ALL carriers lock their devices so that they can only be activated on their networks (either with a SIM card from them in the case of GSM) or with CDMA, on the same network as the phone is branded. There are too many people out there selling phones on line that lead people into thinking that you can use any phone on any network. You can't. You are always better off just buying a phone from your carrier. That way, you get the best price on the phone (since the carrier subsidizes the cost of the device by signing you up for a 1 or 2 year agreement) and also warranties the phone for 12 months. They also support it if you have questions or issues and there is nothing to program to make it work. All these silly Chinese phones and other phones aren't worth it. At least for now, you are always better off just to buy from your carrier. It will save you a ton of headaches, believe me. Thanks. SukiSue