I am a client of the optimus tag service (for English users, it’s a phone plan that includes free calls for any other phone using the same network plan).

Recently, I discovered they have a softphone like system called Webphone (Windows only), that allows you to place and receive calls, SMS, MMS, and other stuff, right from your computer.

My first thought was “this must use some kind of SIP service”. Since the SIP settings are not posted anywhere on the internet, and I don’t want to use Windows to use their client, I decided to dig deeper and try to find the SIP configurations so it can work on any regular softphone.

Although it was easier than I thought (Wireshark, I love you), there is one serious limitation that I couldn’t solve without hacking some open source code. Anyway here’s the main settings:

Optimus Tag SIP settings (to use with a SIP softphone)

• server address: sip.optimus.pt
• username: 351 your number@sip.optimus.pt
• password: your webphone password
• SIP proxy: asbg.sip.optimus.pt
• User Agent: Optimus-SoftPhone/7.0.1.4124

Now, the last item is the worst part. If you don’t specify a User-Agent that starts with Optimus-SoftPhone, you’ll receive a “403 Forbidden User Agent” message. I tried to find a SIP softphone that allowed me to change the UserAgent but didn’t found one (I didn’t try hard).

So I decided to take the Twinkle open source SIP client, changed the hard coded User Agent, and got surprised when it worked flawlessly from the first time! I tried placing and receiving calls and it worked perfectly :)

If you’re interested on the trivial patch (I used Twinkle version 1.4.2) you can find it here.

If you know a SIP client for OS X or Linux that allows me to change the User Agent, don’t hesitate to comment bellow!