I would like to make calls to my FPL number using my SIP URI, and I'm getting some issues. Here is the scenario:
1. I'm using a Linksys PAP2T ATA, recently bought config file with FPL.
2. The phone works normally with the line, I can make and receive calls with no issues.
3. The SIP URI I'm using is 1xxxxxxxxxx@yyy.yyy.yyy.yyy:5060, where xxxxxxxxxx is my FPL number and yyy.yyy.yyy.yyy is my external IP address on my ISP modem.
4. I have a D-Link DIR-300 router between my ATA and the modem, but I've set up DMZ to the ATA in the router. Firewall is also disabled on the router. Ports wide open!

5. When calls are made to the URI on #3, the phone rings normally, but when I pick up the call, total silence (no audio at all on both ways)!
6. After some google searches, I stumbled across this post: http://www.boards.ie/vbulletin/showpost ... ostcount=5. My issue is very similar to what the guy describes on step 5 of his post, so I've also tried to do what he suggests on my ATA configuration:
On the Line tab:
NAT Mapping Enable: yes
NAT Keep Alive Enable: yes
On the Sip tab:
Substitute VIA Addr:Yes
Send Resp To Src Port:Yes
STUN Enable: Yes
Stun Server: stun.freecall.com (I've used this one as a test, don't know if FPL has a STUN server for me to use

The result, when the ATA applies the configuration, is a "Can't connect to login server". Note that undoing the config above, everything works fine again. Can anyone share your experiences with NAT configuration on FPL?
Thanks!