Do all iPhone 4s have sim cards? So they are both GSM and CDMA?

I'm trying to buy an iPhone 4s but was wondering if they All take sim cards.

My friend is offering me a CDMA iPhone but I'm with T-Mobile (GSM Network).
Would I be able to use it on T-Mobile if I got the new sim card? I'm hearing mixed answers and would like to hear a straight answer.

No, the CDMA iPhone won't work with T-Mobile. If they offer you a GSM unlocked or an AT&T iPhone, then you can use it on T-Mobile.

The phone would have to be unlocked in order to work on T-Mobile. All iPhone 4Ss have SIM slots but that does not mean they will work on GSM networks as they are now. I'm not sure how you could get a CDMA iPhone 4S to work on a GSM network though, but I do think it is possible. I say this because right now the Verizon iPhone 5 (CDMA network) is factory unlocked to be able to work on GSM networks.

The only way to use an iPhone for Tmobile is to unlock it. There's currently no way for you to unlock it if it is on a CDMA network through factory unlock. Check out gevey sim cards. They may do the trick, but you will have to be jailbroken in order to use some of them. Check the link below out. I've been dealing with unlocking and jailbreaking for over 6 years. Don't buy anything until you know you can unlock! Good luck.

ps - iPhone 4s and 5 all have dual connectivity when it comes to CDMA and GSM. The previous generations do not have this ability. But the best way to get it to work is a factory unlock.