Choppy line is a common problem when we use sip signaling. The main reasons for the issues are Bandwidth, Codec, Lots of SIP trunks registered, Jitter.
Basic checklist for Choppy Lines
Check the Codec ULAW, ALAW or G729 is allowed on your trunks,If allowed try to use any single codec to avoid choppy lines. For example if you are using G729 then remove ULAW parameter from our trunks. If you are using ULAW then remove g729.This can be done by adding the below parameters on didforsale trunk.
allow=g729 (Use either one of the codec you want)
Next step is to check whether if you have lots of unwanted trunks registered on PBX, as this can cause bandwidth utilization. Remove which is unnecessary
Next thing could be with Jitter buffer.You can enable jitter buffer to avoid this issue. For enabling jitter buffer got /etc/asterisk/sip.conf
and search for jenable and jbforce and uncomment the below parameters.
If still you are facing issues take a tcpdump of rtp ports and send to us.
Command to take tcpdump on linux
tcpdump -i etho -p portrange 10000-20000 > rtpcap.pcap
and send this pcap file to firstname.lastname@example.org