Voicemail box full on jb iphone 3gs

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Hi. I have a jailbroken (spirit) iphone 3gs. The only app I installed was MYWI (tethering app). But now if someone tries to call me and I don't answer they get a message that my Voicemail box is full. I deleted all the voicemail on the phone but still no luck. Anyway to fix this? Thanks.