Panasonic A100 bad reception in Canada

I have a Panasonic A 100GSM Phone, and I've
been having problems with it recently. Sometimes when I make or answer
a
call, the person on the other end of the line can't hear what I am
saying. I can, however, hear the other party fine. It seems like the
audio is not transmitting. In addition, there is always some kind of
static and interference on the phone.

Both of these problems are greatly reduced when I am using the 2.5mm
handsfree
headset. I have a feeling it could be a problem with the built-in
microphone on the phone or some sort of interference.

The problems seems to be worse indoors, but still occur outdoors.
Signal strength has nothing to do with the problem, as the strength has
been at minimum and maximum and the problem will occur either time.

Any ideas on what could be causing this and where I might be able to
get it
fixed?

The A100 is a 900/1800/1900 phone; Canada uses 850/1900 GSM.