Linksys SPA VOIP phone rejects calls from Skype SIP Trunk on Asterisk

Setup

• Asterisk Trixbox 2.6 Server
• Skype Connect SIP trunk to accept incoming Skype calls
• Linksys SPA and Cisco SPA VOIP phones

Issue

Incoming calls via Skype to some Linksys / Cisco IP phones get rejected. Asterisk debug show following reason :

-- Called 715
-- Got SIP response 406 "Not Acceptable" back from 192.168.6.19
-- No one is available to answer at this time (1:0/0/0)

Cause

Issue was caused by enabled Block Anonymous Call option on Linksys SPA devices. On some firmware versions it seems to be enabled by default, on others not.

Solution

This can be disabled in two ways:

1. Via web interface:
   
   • User > Block ANC Setting: NO
2. Via phone menu:
   
   • Preferences > Block Anonymous Call > NO

Asterisk
Trixbox
Skype SIP Connect
Linksys SPA962
Linksys SPA 942
Cisco SPA 504G