does an unlocked cell phone work with t-mobile? ?

[sweetcandy]

i have a sony ericson s500i and it is unlocked. when i got it said it would work with any sim cards. but when i went to a t-mobile store they tried it out and said it didn't work, but i don't think the guy knew what he was doing. can any one help me i real don't want to get another phone

[RichardS]

T-Mobile is GSM provider so it should work. You'll need a sim card from your existing phone, or a new one.