Can an iphone function properly with cingular SIM?

[aphexacid]

When i signed up for at&t in january, i got a SE w580i, because it was free. the SIM in that thing was active for about 2 hours, because i activated my iphone. so the w580i's sim was no longer active.


Now, last week i gave the iphone to my girlfriend, and i figured, ok i will put the at&t sim thats not active in the iphone, and it will activate thru itunes, and switch her number to the new sim.

that didnt happen. i ended up having to use her cingular sim card in the iphone. itunes activated it just fine.

Only thing is, apparently its freezing on her. i know there were a few bizarre moments the first day i activated it, like at on point, all of her contacts disappeared, and then reappeared after a restart.

then, her data was not functioning whatsoever, which was also fixed with a restart.

Do you guys think that the cause of all these problems is because she has a cingular sim card? everything is legit, i've never jailbroken or unlocked it at all.
i used the iphone for about 2 months, and never had even 1 problem with it.

any ideas are very welcome!

 

[zap2]

she should try a restore through iTunes, and see if her problems go away
That be my first step(be sure to back up any important infomation)

 

[aphexacid]

before i activated it with her #, i did a restore in itunes, and i think it re flashed firmware 1.1.4

I can do it again though, no biggie.

But my main concern, is should the phone function properly with a cingular sim? everything seems to be working most of the time, but i wonder if there is some sort of conflict.

Or should i get her a new sim card?