It sounds like you may have an issue with the codec your sip phone is using. When you make a call from the sip phone it picks a codec and hands the call off to the asterisk server. The asterisk server then converts and send it out the TE100XP card. When there is an incoming call, the asterisk box receives it and picks the codec, then hands it off to your sip phone. I would check to see what codec you are using. The best quality will come from ulaw or alaw codec ( also the largest ). GSM and Speex are also ok and about half the size of ulaw or alaw. There are some other codecs that are not free but also work well.