One ATA 186 working like a champ behind a NAt on a Linksys.
Be AWARE!!! I run into some other ATA 186b with older software that still work behind NAT, but with the same exact configuration do not give you any ringback.
One good tip to test ATA behing NAT.
Use the I.P. address of “Dual Talk” gateway to test.
Dial “123” on the phone, plus the I.P. of the gateways.
That will send the call to the dualtalk gateway I.P. just for this call.
You will hear an announcement. Goes trough most NATS like a bullet.