Need to change my voicemail on my iphone 3g?

ok so my crazy ex gf changed my voicemail to say some nasty things and i really dont know how she did it cuz she had no access to my phone what so ever but i cant change it idk how i go to voicemail then greeting then i made a custom message and saved it and it still wont change. please helpNeed to change my voicemail on my iphone 3g?idk... but if it does not work like that then i think you should call att and ask them to change it for you