I have a DXP Plus with two T1's. They were working fine 3 months ago. Now they have echoing on some calls and some calls get dropped. Replaced one of the T1's cause it stopped working. Everything works except that we still have echoing and dropping of calls. Today some callers can not be heard on incoming calls. When customer calls back after about 3 times then the call works good. This will happen on either of the T1's. Any suggestions? Carrier says it's a PBX issue.

I know that on Panasonic that is about 99% a clocking issue.

Pull your status logs with hyperterm. It'll show what issues the T1 circuit is seeing.