Well, the good news is that the sudden interest in VoIP means that a lot of the equipment you need that used to cost a fortune is now available at consumer prices. Let's go through it.
Hooking up to the PSTN
The PSTN - public switched telephone network - is the name for the international telephone network we know and love. You'll want to route calls in from it, and out to it. You might even want to play around with a number of different systems to get the best value for money.
If you already have an existing telephone line, and want to use it, the easiest method is to use something called an FXO. An FXO connects to a telephone line and routes calls to and from it to your PBX. Any recommendations? Well, I haven't tried it, but the Grandstream Handy Tone 503 is a low cost device that includes both an FXO and an FXS in one package. What's an FXS? We'll get to that in a moment. The HT503 routes calls from the phone system to your Asterisk PBX via your Ethernet network, and uses the industry standard SIP protocol, which is Asterisk's second language (after IAX.) The HT-503 costs around $60 at the time of writing. Another option is the Cisco SPA3102 which has roughly the same capabilities.
If you don't already have an existing telephone line, or you'd like to migrate to an entirely all-IP network and get rid of your phone line, you also have a number of options.
One ultra cheap, but not quite ready for prime-time, system is Google Voice. Google Voice offers VoIP using a system called Jingle, and Asterisk includes native support both for Jingle, and for Google Voice's version, which includes a few quirks.
You can also use Google Voice using an intermediary. IPKall offers a free incoming phone number, one based in Seattle. You can configure Google Voice to call that number, and also configure Asterisk to both accept calls via that number, and when an outgoing call needs to be made, have Google Voice call the number and route it via that. You can use this system if you use an older version of Asterisk. The entire system is transparent, but it's somewhat ugly, and I'd question whether anyone wanting a reliable phone service should use this system. Still, configured correctly, you can have a phone service that works just like a regular phone system, but one that costs no more than your existing Internet connection.
Free is free, and it always comes with some health warnings. In particular, bear in mind that you don't get 911 service with the above system. So if you're planning to go the free route, make sure there's other options. A prepaid cellphone will do the job.
Talking of cellphones, you can also use a cellphone that has Bluetooth capabilities with Asterisk. Calls can be routed via the cellphone, and received via the cellphone, as long as it's within range of your PBX, and you've compiled and installed the necessary add-ins to Asterisk (and, naturally, you have Bluetooth on the computer that runs Asterisk.) I'm wary of this route, as Bluetooth is great in theory, but often leaves a lot to be desired in terms of reliability, but it's certainly an option. If you have a family plan with unlimited calling, you could add a line, and use that.
For paid VoIP services, there are many, many, VoIP providers. Expect to pay around $10 per month, sometimes less, sometimes more, for a provider that offers SIP. Be very aware that there are a lot of frauds out there, companies that exist solely to rip off the big telcos, and while you might not be concerned about AT&T's bottom line, being disconnected and without phone service unexpectedly can be a major problem.
For a relatively trustworthy source of recommendations, I suggest BroadbandReports.com. Be careful, as a lot of websites that promote themselves as unbiased are actually run by the providers themselves.
What do I do? Well, I signed up with a company that offers SIP phone service, and I route my US calls via them. My international calls are routed out using Google Voice.
Hooking up your own phones
So that deals with the outside world, what about actually hooking up your own phones to the Asterisk server? You have a variety of options. The option most people start out using is a so-called "Soft phone", a SIP client that runs on their PC, but nobody wants to have to sit at their PC when they make and receive phone calls.
You have at least four low-cost options when it comes to hooking up phones to your network, you can use any or all of them. We just mentioned Soft phones, but what are the other options?
The most obvious is an "FXS", a device that hooks up a regular telephone - with an RJ-11 jack - to your network. There are many options here, all of which provide one or more RJ-11 jacks, each individually configurable to act as a SIP client as far as your PBX is concerned.
- The Grandstream HandyTone 502 is a very low cost VoIP adapter that's proven to be immensely popular, not least with VoIP providers themselves. Expect to pay well under $50 for this device. Grandstream also offers the HandyTone HT286 which only has a single port, it's a little cheaper if your needs are more modest. And as I said above, the Grandstream Handy Tone 503 is another option that combines an FXO and FXS in one box.
- Cisco/Linksys offers a range of FXSes including the Cisco SPA2102 and the Cisco PAP2T. And, as I said above, the Cisco SPA3102 combines a single FXS and an FXO. Expect to pay between $50 and $70 for these devices.
All of the above devices are configured using a web interface, and do not need special software installed on a PC or anything like that.
Option three: use a phone system that supports VoIP out of the box. Siemens offers two DECT cordless phone base stations that support SIP directly - as in you plug it in to your network, bring up a web browser, enter the details of up to six SIP accounts, tell the device which handset uses what and when, and then, well, it just works. I recommend the Siemens Gigaset A580IP based upon my own experience with it, it's very low cost for what it is, and works well with most of Siemens' other DECT handsets.
Option four: Android. Android Gingerbread includes a SIP client built-in, and prior versions of Android can have a third party SIP client, like Linphone, installed. While trying to make this work over your cellular connection may, ultimately, not be worth the effort, you can effectively turn any Android cellphone into a cordless extension phone when it's on Wifi in your own home.
And not just Android cellphones. Android is becoming a standard operating system for MP3 players, most of which are open enough to support the installation of SIP clients.
In fact, any tablet or portable media device that is capable of running a SIP client, that has a microphone and speaker, and has a Wifi connection, is capable of being an extension on your phone network. Useful to know if you have an old Nokia tablet running Maemo, for example.
Something I invite you to look into: The Archos 28 4 GB Internet Tablet (Black) is $80, and in theory has the spec necessary to make it into a very cool cordless phone. I'll be curious to hear your experiences using it.
What are your experiences of the above devices? Did I miss anything you think is worth recommending?
(All of the above links are Amazon Affiliate links, I get a small kick-back if you buy from there, but this only factored in to my decision to link to Amazon, not in my choice of products! And I'm sure you wanted to know where to buy these from anyway!)