HI All, Just bought a 3gs from Craigslist yesterday. They guy had it unlocked and has his SIM installed and I saw the Tmobile bar with his SIM. HOwever today, when I put in my Tmobile SIM...its not detecting my SIM. I have been using my tmobile SIM on my 2g for a year with no problems. I have the guy's old SIM and when I put his SIM in it then the phone detects it. Do I have to change some setting for it to read my SIM?? And for some reason I cannot power off his phone to make it come up and read my settings.