Call to certain cell phone numbers will not go through

[haahoo]

I set up the Magic Jack. The only issue I have is it will not ring my two AT&T cell phones. When the MJ places a call to one of the two cell phones, you can hear in MJ it rings about 4 times and then stops. The cell phone never rings (seems like the call never makes to the cell phone). But I have no problem placing the calls from the same cell phones to MJ, and MJ will ring, and then connection can be made. I also have a VOIP phone at home, and no problem with outbound or inbound calls from or to MJ. I have verizon FIOS internet with wireless router at home. I tried on another wifi hotspot, and found the same issue. So it is not my home internet problem. I also tried to call my relative's cell phones (VERIZON and AT&T), no problem!
I contacted tech support at MJ, and we tried upgrading software, adding new ports, and shutting down antivirus software as well as different USB ports. Nothing worked.
It was strange that when I shut down the aitnivirus software, only one time the call to one of my cell phones went through. But I could no longer repeat the success.
Also when I used another wifi network, there was one-time success only.
It seems like the success is by luck like winning a lottery. 99.99% is not success.
I am puzzled by this problem, and not sure where is problem lies. I do not expect MJ tech support can solve my problem any time soon.
Anyone knows how to solve this problem, please help.