I have VOIPBUSTER working on X-LITE and this is how I did it. I hope this will be of help.
Thanks to Dean for publishing the images.
I set up X-LITE for VOIPUSER first and tested it. Once I was happy I then setup GOSSIPTEL and then setup VOIPBUSTER. I normally receive calls on the VOIPUSER number and my GOSSIPTEL number works as well. I have not used VOIPBUSTER for I/C. I use all three for O/G mostly VOIPBUSTER but I also use GOSSIPTEL to make all sip calls. I keep my use of VOIPUSER to a minimum O/G.
To setup VOIPBUSTER open the <menu> on X-LITE and then select <system settings>, <sip proxy>. A list of Proxies will then be displayed. Select the first spare proxy (in my case proxy 2) and double click it.
The following window will be displayed.
Scroll down to see all the settings
The key settings are:
Enabled YES
Display Name (VOIPBUSTER user name)
Username (VOIPBUSTER user name)
Authorization User (VOIPBUSTER user name)
Password (VOIPBUSTER password)
Domain/Realm sip.voipbuster.com
SIP Proxy sip.voipbuster.com
Out Bound Proxy sip.voipbuster.com
Dial Prefix (I left this at #2 and you have to add #2 to the front of the TN to make a call using VOIPBUSTER)
I left all other settings at the default.
When finished I clicked the back button to save the changes.
The only other change I made was to click on the GSM on the phone so that it was disabled (greyed out). This stops the VOIPBUSTER call going out at GSM quality (see other posts).
This works fine for me and I hope it helps you.
Mark