I got mine to work and so far I have about 12 hours with no problems. This is up from 20-30 minutes before.
Here is what I did:-
1. Upgraded to R072
2. Changed IP addressing scheme from 10.10.10.x to 192.168.1.x (Unlikely to fix the issue)
3. Increased the DHCP lease time to 10080 minutes (Not certain how much of a factor this might have been, but was quoted in an article about resolving MagicJack+ issues).
4. Assign a static IP to MagicJack+ (This would be needed for the next step).
5. Implemented DMZ for MagicJack+ (This definitely did the trick before, however it would work for 20-30 minutes and then drop again).
6. Disabled the 5Ghz network (I believe this may have played a role in stability in conjunction with number 3).
I had previously attempted to use the port forwarding but it seems as if MagicJack+ uses a range of ports from 10000 to 65535 in addition to 5060 and 5070. Port Forwarding never worked for me.
Also I switched the MagicJack settings (through the Magicjack login) back to DHCP and this worked.
You can probably go without step 2 and 3 above, and see if that works.
I will continue testing on this configuration for another 2-3 days and then re-introduce 5Ghz and see if I get problems.