Cut-offs with the Treo 270

[rmandler]

Lately I'm having a problem with my Treo 270 that during conversations I'm hearing clicks and being cut off temporarily (for periods of half seconds) from the other side when using the phone.
As I've got another phone (Nokia 6310i) which I can use with the same SIM
and line and it does not make these kind of problems, the service provider
claims it's an instrument issue and not a line problem.

I would like to know if anyone has encountered such a problem and what might be the solution.
I would like to add that the symptom I've mentioned of clicks and cut-offs are
ONLY in the normal use of the phone. In case I use the Speaker Phone or the
Earpiece this problem does NOT occur!
Thanx
RM