Has anyone took a unlocked sprint iphone and used a t-mobil sims cards in it?

If you have does it have alot of drop calls and does it work okay? Is there any cons about it?

Standard sprint phones are CDMA only and incompatible with T-Mobile, as they are a GSM network

Sprint does have some World phones (iPhone 4s, iPhone 5, most blackberries) and these will work on any GSM or CDMA network, but will need to unlock it… It should work just the same for calling/texting as a t-mobile phone.

the iPhone 4 from sprint is CDMA only and not compatible.

also as of January, its illegal to unlock your phone yourself in the US, just a heads-up

That totally depends on how the phone's been unlocked. But you won't get 3G on T-Mobile as T-Mobile doesn't support the 3G bands of iPhone yet, only works on 1700MHz. They'll soon get the 1900MHz so you'll get 3G service soon on your iPhone.