Step 8. Register your phone number at

The whole idea of this cookbook is to make HD Voice phone calls. But as described in Step 7, the way that virtually all phone calls are addressed is with regular phone numbers, called E.164 numbers. The problem with this kind of addressing is that the easiest way to complete calls is via the PSTN, which always busts a call down to a narrowband codec – PSTN gateways usually negotiate G.729, which is marginally poorer in quality than G.711 which is how calls travel once they are on the PSTN.

The way to avoid passing through the PSTN is to address calls with SIP addresses as described in Step 7, rather than E.164 addresses. But what if you want to call someone but you only have their phone number, not their SIP address? There is a technique called ENUM (E.164 NUmber Mapping) that uses a database to translate from E.164 to SIP addresses. Actually there are several ENUM databases. ENUM is patchily deployed; some countries have a strong ENUM implementation, others not. The statuses of the various countries’ ENUM deployments are documented here.

You can add your phone number to an ENUM database at You can verify that it is working correctly here or here.

I added the number of my POTS (Plain Old Telephone Service) line and associated it with the address of my IP 650 phone. That way when people dial that number from a regular phone it rings on my POTS line, but when someone calls that same number from an IP phone it rings on my IP phone. In theory. Actually, not all VoIP providers do the ENUM lookup, because it adds a few seconds to the call setup time. Gizmo5 does (it calls it Backdoor Dialing), OnSIP doesn’t.

3 Replies to “Step 8. Register your phone number at”

  1. In the Netherlands all PSTN uses G7.11.
    However only 60 entries in ENUM and they are only mobiles, reverting to G.729. And registering costs 7 EUR for mobile, 17.50 for localased e164. Nonen entered yet.

    All Voipers revert to PSTN for touting.

    G.722(both of them, 10 and 20 msec) on 650’s is great, ONLY if it is an SBC to SBC contract. Otherwise back to e164 andn G.711. Lamentfully.

    I realy appreciate your site and the ability to just comment without logging in or so. You have done a great job!

    I only have a Polycom 610

    Greetz, Ronald

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