i had a tmobile payg sim from about 2 - 2 1/2 years ago that i put back in my phone and it still worked, with the exception of it needing some credit (use it all before it stopped using it as i went onto contract) not sure whether this still applies , you could try calling t mobile customer services for an answer to that.
EDIT... Have just spoken with T Mobile - they said i was lucky re the above - was advised that for the line to stay active you will need to make a chargeable event once every 6 months. by chargeable, thye mean send a text, make a call - something that takes a little credit off the balence. If no chargeable events made in the 6 months, they will asume the phone is not being used and will place it into 'hibernation' and a text will be sent to the phone advising this. From there, the user will have 90 days to re active the number( not sure how, she didnt explain, but am assuming you make a call/send a text) otherwise the number will be recycled (taken off the sim)
Last edited by bluechang : 20-01-2007 at 15:56