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:RaisesHand: A girlfriend on Verizon and myself on ATT were having this problem when I had a 3G. I changed my number and got a 3GS and don't have the problem.
 
I have a 3gs and I don't wanna change my number

I don't mean to confirm that fixed things. It resolved itself over months. I just recall a period where she'd be upset that I 'ignored' her despite never getting a text.
 
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