I had the same problem about a year ago when I tried to use a SO SIM from a Nokia 1600 in my Samsung X475. I took both phones back to the 7-11 and managed to get them to swap the SIM from another 1600. That SIM works just fine. The only difference between the two SIMs is that the one that works has "U0.2" following the serial number. From what I can determine via Google the "U0.2" indicates a newer SIM.
In my case I hadn't made any phone calls on the non-working SIM so there was no problem with swapping it. You may have problems if the SIM has been used, i.e. there is less than the original $5 airtime on it.
The only difference between the two SIMs is that the one that works has "U0.2″ following the serial number. From what I can determine via Google the "U0.2″ indicates a newer SIM.
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