I have a very strange problem trying to get an Aastra 6751i working with Voiptalk and a Vigor 2820n.

The phone registers properly with Voiptalk, and I can receive incoming calls. However, outgoing calls don't work unless I disable the Data Filter altogether in the firewall settings of the Vigor. I've tried opening up all the ports recommended by Voiptalk, but that hasn't helped; nor has disabling SIP ALG via Telnet, which I know has been the source of problems for some people.

What's particularly strange is that the Data Filter has only one rule, which is the standard 'block NetBIOS' rule. If I remove the 'active' tick under that rule, then as far as I can see there shouldn't be any blocking going on at all (there shouldn't be any active rules) - but even then, I can't make outgoing calls unless I disable the Data Filter altogether.

Softphone apps on my iPhone (Fring, SIPphone) work fine when connected via my network.

There must be something about the operation of the Firewall itself, rather than any port blocking, that's interfering with the Aastra's ability to make outgoing calls - but I can't for the life of me figure out what. Any ideas?

Many thanks.

I've seen this on another site with dv2710 & Aastra phones, & another site today mixed panasonic IP PBX & Linksys ata's. Seems to be when multiple devices are trying to register outbound. Haven't put any engineering time into finding the root cause but if any has already done this please post your findings (lazy admin).

TIA