You should be OK as the PAC will just become out of date and your contract with T Mobile will continue as they still 'own' that number. My PAC from vodafone ran out at the end of last week but my xperia is still functioning OK, i am not sure when to request a new PAC as i have no idea when the device will finally arrive. I keep thinking that if i get a new PAC it will definetley arrive within 30 days but then i get that nagging doubt that it will still be delayed.