Hi yes your metro pcs sim card will work in t-mobile g1 phone only if it is unlocked one ..Else if the phone is locked to t-mobile network then until you unlock it you can't use it with metro pcs sim ...If you want to unlock your phone then have a look at sites like Theunlockspot.com here they render unlock code for all mobile models at reliable cost ..After unlocking your phone you can freely use it with metro pcs sim card ...