BB Curve :: Phone Calls Constantly Breaking Up

For at least the last 6 months I've been having a constant problem with making phone calls from my blackberry. Whenever I make a call more 99% of the time I have problems where the person's voice on the other end of the phone is constantly breaking up.or the voice sounds distorted (the only way I can really describe this is that it sounds almost like someone's playing the sound back in slow motion with a lot of inteference noise mixed in). Other times I have attempted to make a phone call and after waiting to hear a ringtone while the screen reads "connecting" for a while, I get the "call failed" message. I would put these problems down to bad signal but when I make the calls my phone always has at least 3 bars of signal. At first I wasn't sure if the problems were from my phone or whether it was from the phones I've been calling, but today I've called 3 different numbers and had exactly thesame problem with it.