Shaking loose from the Public Switched Telephone Network (getting to know SIP URIs)

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It is ingrained in our behavior that if we are going to take a step toward calling someone on the telephone, we need to ask them “what is your telephone number?”  It is is ingrained in our behavior that if we are going to make it possible for someone to call us on the telephone, we need to be able to tell someone “our telephone number”.  This world of “having a telephone number” and “calling a telephone number” is the most prominent aspect of the Public Switched Telephone Network (Wikipedia article).  One way to think of the PSTN is that it is a collective effort by governments and post offices and landline telephone companies to collect money from people who “dial telephone numbers” and who receive telephone calls from other people who “dial telephone numbers”.  

The rise of the Internet has prompted many efforts to find ways that people can talk to each other without paying money to the PSTN.  One of those ways is the SIP URI (Wikipedia article).  There are two ways to think of SIP URIs:

  • Incoming calls.  It is possible in the year 2020 for a person or a business to set up a SIP URI (or dozens or hundreds of SIP URIs) to be able to receive incoming telephone calls.  Depending on how you set it up, such incoming calls can be free of charge to receive or extremely inexpensive to receive.
  • Outgoing calls.  It is possible in the year 2020 for a person or a business to place telephone calls to SIP URIs.  As a general matter, such outbound calls are free of charge to the caller.

The alert reader will immediately point out that lots of people have been making free phone calls all over the place using the internet for many years now.  What’s the big deal with SIP URIs?  Yes, people have been making free phone calls on Skype and Whatsapp and Wechat and Viber and many other internet-based systems.  But those systems generally work only if you are using “an app”.  They generally work only on smart phones.  As a general matter you can only use such a system to talk with someone else who “has an account” on the same system, and who also has the app installed on their smart phone.

SIP URIs have the prospect of providing a nearly seamless way by which ordinary phones like you might have on your desk in your office or at home, phones that mostly get used on the PSTN, can also be used for talking to other such ordinary phones.  But without the need of paying money to the PSTN.

Take a look at our firm’s “contacts” page.  You will see that we list a SIP URI for calling our office main telephone number.  Our contacts page says:

PSTN: +1 303 252 8800
or
SIP URI: 11218027088@sip.oppedahl.com

This means you could “dial our telephone number” which is 303-252-8800 in the United States, and the call would enter our PBX and we would receive the call.  If you are located outside the US, this call would cost you some amount of money per minute.

But another option is that if you can figure out how to do it, you can place a call to “11218027088@sip.oppedahl.com” and it will be a free call.  That call will enter our PBX in the same place that a call to 303-252-8800 would enter our PBX.  It would get handled in exactly the same way.  Oh and not to put too fine a point on it, but the call quality can be just as good as that of a PSTN call.

I say “if you can figure out how to do it” because, dear reader, I imagine you would tell me, if pressed, that you don’t have any idea how you would place such a telephone call.  If you can figure out how to do it, it will be a free call for you, no matter where you are in the world.

With our PBX, one way that we place such calls is by putting the SIP URI into the “address book” of our PBX, associating it with a “speed dial” number in our PBX.  So for example in our system I can go to any telephone in our office telephone system and I can dial *7526 and this is a speed dial entry that calls the SIP URI 11218027088@sip.oppedahl.com.  You might find that your phone system has the ability to set up speed dial numbers that call SIP URIs.

If you have a VOIP app on your android phone, you can probably call SIP URIs right now.   Maybe you use Zoiper or Wave, or any of the lots of other well-known VOIP apps.  Anyway, you open the app and in the place where you would normally type in a telephone number (from the PSTN) you simply type in the SIP URI (for example “11218027088@sip.oppedahl.com”).  And I think you might be astonished to find that the call will reach our law firm.  And it is a free call no matter where you are in the world.

What might reinforce this for you is that the Android address book has a field where you can enter somebody’s SIP URI.  See the screen shot quoted at the beginning of this blog article.  So you could store a SIP URI in the address book, then open your VOIP app, and look up an entry in your address book, and if there is s SIP URI in the SIP field for that entry, it will auto-load into your VOIP app, and you can dial it.

On our contacts page you will also see dial-in information for our telephone conference system:

PSTN: +1 303 653 9157
or
SIP URI: 11218027057@sip.oppedahl.com

This once again means that you could dial a PSTN number 303-653-9157 in the US and it would reach our telephone conference system.  But you could also call the SIP URI 11218027057@sip.oppedahl.com and your call would reach the exact same place — our telephone conference system.  If you call this SIP URI from your office telephone system, the quality of the connection is very likely to be just as good as the quality of the connection for the PSTN call.  In fact the quality of the connection with the SIP URI might be better, depending on what service you use for your PSTN calls.  And the SIP URI call will be free of charge from anywhere in the world.

Please try calling the SIP URI for our conference bridge system — 11218027057@sip.oppedahl.com.  If you figure out how to dial a SIP URI from your office phone system or from your smart phone, please share a few words about it in a comment.

One thought on “Shaking loose from the Public Switched Telephone Network (getting to know SIP URIs)

  1. Pingback: Migrating from a physical local PBX to a cloud PBX - Ant-like Persistence

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