Complete list of SIP URI + PSTN ITSPs

Started by SeanTek, June 29, 2020, 02:11:13 PM

Previous topic - Next topic



I would like a complete an updated list of ITSPs that support SIP URI calling as well as PSTN. I discovered that some providers such as Ooma (and, frankly, Google Voice) do not support SIP URI calling, and there is no longer any obvious way to get it to work again.

Ideally I would like to call a PSTN (E.164) phone number from my IP phone and have it automatically call with wideband audio, encryption, etc. directly over the Internet, for phone numbers that are similarly situated (i.e., VoIP-based). I have come to understand that this is mostly a pipe dream and that it would only work these days in one of two circumstances:

  • Both you and the callee are on the same ITSP (e.g., Callcentric-to-Callcentric), and the carrier also supports direct VoIP calling without pretending that it's a PSTN connection.
  • Call using a non-PSTN (meaning not E.164) phone number, such as a SIP URI, a direct IP address, or non-public phone number unique to the ITSP.
  • Call with a PSTN phone number but manually configure your VoIP account or VoIP phone to rewrite the number with a dial plan to a SIP URI or something similar.

The second point means that no "average" telephone user would ever use it. The third point means that only IT admins (or nerds) who are determined enough to make it work for average users will be able to get this to work, but then it is an administration nightmare that only works as long as two organizations continue to use the same ITSP or VoIP configuration, and stay in contact with each other. It only makes sense to go to this effort if one huge organization (e.g., the Army) wants to route all its calls to and from another huge organization (e.g., the Navy) and thereby save millions of otherwise-billable minutes.