ppp-troubled

[E.P.S.]

When calling through my 56k-modem sometimes (not very often) the modem misses 
a number (por example, it does 5-6-9-1-silence-3-4..). While being connected 
to my isp sometimes the CS switches off for a few seconds; also when de modem 
is transmitting/receiving x aplications take long time to load (like 5-10 
seconds, which is really annoying in a Pentium IV), or even executing. I 
thought maybe all these things are related. It happens both using ppp and 
pppd, using freebsd 5.1. Is this logical?

Thanks in advance