Treo Outgoing Call - Help -

[AFLunatic]

For some reason.. sometimes when I'm making an outgoing call, instead of the normal ring, I'll get a distinctive tone that beeps until the other party picks up. Even if the person i'm calling has a ringback tone it will give me the weird tone and then halfway through the call being made and the person picking up the ringback tone will come in... but sometimes it just goes mute after the weird tone rings and i can't hear anything until they call back or I try again. This is VERY annoying and it's killing me any help please? I'm using a cingular branded unlocked Treo 680 on the T-Mobile network.