I had a lot of problems with several sims, but im happy to say my 3G has been working without any problems ( everything working - no reboot required) for over 6 weeks now.

Firmware: 2.1
Sim Cutting: YES
How long have you had it running: 6weeks +
How long does it take to pick up: below 10 seconds
Any trouble taking SIM back out?: no problems
General comments: very happy!
Link where you bought: www.iphone-sim-unlock.com
Price: $37,95

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Yessim SIM
calls, sms, data in/out: working
GPS: NOT working
Signal Loss: YES
Final Verdict: Fail

i-Smartphone SIM
calls, sms, data in/out: working
GPS: working
Signal Loss: YES
Final Verdict: Fail

iPhone-sim-unlock.com SIM
calls, sms, data in/out: working
GPS: working
Signal Loss: NO
Final Verdict: PASS - Working since 09/13/08