I just came home and tried some things.
First i activated SIP proxy and changed the UDP port range so that it does not match the one of my VoIP device. I saved changes and then deactivated again the sip proxy after that my VoIP device failed to register with my VoIP provider, even rebooted it failed to register.
Then i rebooted m0n0 and everything seems to work fine for now, the issue where the VoIP device still occurs.... Weird..... If i unplug the VoIP device, and look at my m0n0 and DSL Modem LEDs i can clearly see that m0n0 is sending data to my VoIP provider....
After that i saved my config file, edited the file and killed the whole SIP section. I restored to defaults and uploaded again my cnfig file, but this didn't help !
Should i try to downgrade to 1.3b4 and then try to upgrade to 1.3b5 and test further ?
Edit : I downgraded to 1.3b4 and it works fine......
Edit 2: I Reupgraded to 1.3b5 and tried to reproduce the issue, and it does not occur any more....