VOIP is legal in qatar for personal and business use (Legal to use) and I am using it since long time BUT it has been very unreliable since probably couple of weeks

You should disconnect your ADSL to change your IP address and then try again, and that could work with you for a single call, once you are done with the call you need to do this again..

Also another way is to change the port (if you know how to modify the client configuration) from 5060 to 5061 and try then back again.

Usually voip providers has their servers running on both..

Receiving calls should be a problem, I think qtel is reshaping the packets so that you may not be able to initiate calls,

At least this what I have noticed,

Issam