It's certainly a possibility. I kept looking at everything on the PBX and handset side and once I verified it was and looked ok put in a ticket with the carrier who assisted in the troubleshooting process and found the problem to be on the trunking server I was connecting to (though it had been working for some time before that). They made some changes apparently, I was moved to another primary and secondary and the problem went away and has been fine since.
I only had the issue with one of the trunking providers. Do you have multiple providers that this is a problem with? Worth a try asking the provider.