There are many countries which are facing the voip block problem.
Generally, there are several means to block the voip business:
1. block the IPs and domain names of servers which have the main Voip stream.
2. shield the main Voip server ports, for example the 5060 port for SIP protocol, or the 1720 port for H.232 protocol and so on.
3. monitor the Voip stream, if detected, send out the fake IP packages to disturb the Voip communication.
4. a lot of Middle-East countries like Dubai shut up most of the ports , only letting free limited ports such as 80 port.
There are 3 ways to resolve this problem:
1. use VPN. The flow picture is as follows:
2: use private protocol on the voip gateway, such as Xia304, Shang 308, Shang 332 which are our products. By using our private protocol, you could use voip freely, no body will know you are using voip. What they can see is some TCP stream. However, this can work on our gateway only.
3. use our voip antiblock module for asterisk(a free software available at http://www.asterisk.org/). After that ,you can set up a platform, to manage all of your terminals, which use our private protocols to communicate. But for outside, such as landing, the devices still use the standard SIP protocol. 
