SIP Phones

Edition 3 - updated 14 Apr 2007 4:26 pm.

SIP is an internet protocol that supports making telephone calls across the internet. 

Whilst the SIP protocol can be run through a PC, this article deals with using a piece of hardware to enable a standard phone to be connected to a broadband router and used just like an ordinary phone except that the calls are either free or very cheap and they travel over the broadband link rather than the telephone circuit. Hence it has no impact on the user's standard telephone.

At the time of the first edition of this page, SIP calls could be obtained for free, now most service providers are charging for calls but usually the calls are really cheap worldwide - many can be had for 1p per minute - and there are still some free destinations - it changes every few days so it's worthwhile checking to see which supplier is cheapest each week. I tend to switch between SIPDiscount and VoIPCheap. N.B. there are two VoIPCheap sites - (a) and (b) .com - the latter having appeared since Edition 2 of this page was written. Although the no longer offers free phone calls for the UK, the newer site does offer free calls to the UK and many other destinations provided that you purchase some credit up front (currently 10).


Many people think that Skype must be something to do with SIP, but actually it is not. True: Skype can make calls to land lines as well as to other online Skype users; and it is true that you can buy a really good Skype cordless telephone that works both with Skype and your land line; but nevertheless Skype does not use SIP technology - it uses technology of its own devising.

With SIP you can buy a SIP phone and connect it directly to your broadband router, or you can buy a SIP adapter that will let you connect an ordinary conventional phone to your broadband router, after which you can then make internet calls just as if you were making an ordinary phone call - no PC is involved and the experience is just the same as using the phone in your home. The difference is that if you choose your SIP provider wisely then you can make most of your calls absolutely free!!!

SIP Adapters

I use a Linksys adapter that has two telephone ports on the back allowing effectively two independent SIP telephone lines and this plugs directly into the router. I bought this adapter from and it costs 44.05 incl. VAT. The phone ports take US style phone plugs so I also needed to buy a couple of UK-US phone socket adapters which are available from the same source.

The Broadband Router

Many people operate their broadband with a simple ADSL modem or cable modem that connects directly to the PC with a USB cable. It is not possible to connect other devices into that style of modem. If you have that style of modem then you would need to replace it with a proper router. For example...

The Linksys WRT54G wireless broadband router will connect directly to a cable modem and from there the PC can be connected either wirelessly or through one of the 4 auto-speed auto-reversing RJ45 network ports on the back of the unit. The unit itself is easy to configure, has a RJ45 network port especially for the cable modem and offers a protective built-in firewall. The whole unit is easily configured either using the s/w wizard that comes with it, or through its built-in web browser interface. This can be purchased from DABS for 47.53 incl. VAT. Similar products exist for ADSL (rather than cable) connections.

SIP Service Providers

Just as one needs an Internet Service Provider (ISP) in order to access and use the internet so one also needs a SIP Service Provider to be able to make SIP internet phone calls. There are several of these around but they vary enormously in what they charge.

If you're going to use both lines then you will likely need two service providers. I would recommend the two that I use and they are SIPDiscount and VoIPCheap.

Both of these providers work in a similar way: you pay a small subscription which lasts 90 days. The prices of phone calls vary from day to day so it's worthwhile checking on your provider's web site what their rates are today before making calls. Often phone calls to standard UK land lines are free - they disconnect after 1 hour but you can then hit redial - these used to be free for both of these suppliers but now it's mainly SIPDiscount that is free to UK numbers. Phone calls to many land line destinations throughout Europe are also often free. Phone calls to USA land lines and mobiles are often free. Other destinations incur a charge but the charge is very reasonable, although sometimes they can be free too - for example: VoIPCheap is currently free to Australia and they charge 1p per min to UK numbers. Mobile destinations are significantly cheaper when compared with a land line: for example they tend to be around 9p per min including VAT compared to 28.5p per min plus VAT. At the end of 90 days any unused credit is lost and the account needs to be credited again. Currently SIPDiscount requires 10 credit and VoIPCheap requires 10 credit. Both are excellent suppliers and very reliable with high quality connections.

Configuring the SIP Adapter

The handbook says that it can be configured using DTMF tones from the phone. I found that to be impossible when trying to configure it for these sites. In the end I used DTMF tones to assign the device a fixed IP address on my network and then I opened a browser using that address and the internal web configuration panels appeared. On the right hand side of the panel choose Admin Login and then in the menu choose Line1 (or Line2) as required. N.B. the default admin user is called admin and the default ordinary user is called user. On the service provider's web site it will tell you the SIP parameters; match them up to the form that you see and fill in the relevant ones. These were...


In my case, on the Router, it was necessary to open up some ports. Using the browser to configure the router, and choosing the Gaming panel, I needed to route the following ports to my SIP adapter:-

bullet5060-5061 UDP
bullet53-53 UDP
bullet69-69 UDP
bullet10000-20000 UDP

After that everything was up and running and working just fine.

CLI and Incoming Calls

Many people now have CLI (Caller Line Identification) where they can monitor the incoming caller's number before they answer the call. Both SIPDiscount and VoIPCheap will provide an incoming telephone number for free. In my case both of these numbers were for my local area - Nottingham. SIPDiscount relays this number in the CLI so the called party can recognise your number; this is also useful in case they miss your call and wish to use 1471 to call you back. Unfortunately, VoIPCheap does not relay the number and the called party simply sees International.

VoIPCheap also offers a PC service. If you are logged on to the PC service then the SIP phone on the SIP adapter line will be disabled and incoming calls will ring at the PC. Once you log off from the PC then the SIP phone will recommence operations after 5 mins or so.

Some Final Thoughts

I'm saving around about 100 a month in phone costs using this scheme.

If you connect good quality DECT (Digitally Encrypted Cordless Telephone) equipment to the SIP adapter then you can use it all around the house and garden instead of needing to be close to the router. You can buy these loudspeaking and with built in digital answering machines with a spare hand set and charger with set-to-set intercom now for 26.

The quality over SIP is excellent. Although I'm a big fan of Skype, many people say that Skype suffers from poor quality and Skype will likely tell you that this is low bandwidth on your broadband when in actual fact it is usually the sheer load imposed upon the PC that cannot cope with it. These SIP phones never vary in quality not even when I'm downloading music or video across the broadband.

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