For your missing audio issue, do you have MTP enabled on the remote phones?

If you are using CCA, check "Use as Teleworker Phone". If you are using the CLI, input "mtp" under the ephone configuration for each phone.

Also for your 3100 extensions if you are using CCA, look under "Troubleshoot" -> "Telephony Diagnostics" -> "Dial Plan Test". This lets you test out different numbers to see how the dial plan interprets them.