Cannot recieve messages

Well it's a friend's phone, and recently she has started to have a problem in which she could not send messages to certain people. I've searched through all of the features, defaulted the phone multiple times, and tried different settings to try and figure the problem. She cannot send a message to my V3, or my friends Ericsson T226, and all phones are on SunCom wireless. I've tried customer support, but they tell me that it's her phone, and they cannot do anything about it. I can send messages to her phone, but if she tries to reply, I recieve nothing.

EDIT:
I found this quote, could this be why I don't get messages from her?

But I can recieve messages from many other people, some are on SunCom.

She should call customer support and ask them about her service. Some companies won't put outgoing text messages unless a person wants them. She also needs to make sure all her settings for outgoing messages are correct. What kind of phone is she using?

Oops damn, she's using a 6062 Nokia. I've gone through all the settings, and defaulted all the settings back to factory, but nothing seems to work. I've called customer support, and they say it's her phone not their service. The only thing I can think of that I haven't tried is adding a 1 infront of the number, but I don't what difference that would make.

Before when I was on cingular I could recieve messages from her 6062 fine, and I was using a 6020. I guess it might be a phone conflict between my V3, and her Nokia?

what kind of phone she is using?
it may its software make it format or update it. good luck