I have now fixed this issue, and am posting this for the benefit of anyone else who may be suffering with a similar problem.
It was, as I suspected all along, a subtle misconfiguration at this end. The fix was to give the SIP trunk its own configuration stanza in sip.conf as follows; [sip_trunk_outbound] type=peer host=provider.sld.cc disallow=all allow=alaw and replace all instances of Dial(SIP/provider.sld.cc/44${EXTEN:1}) with Dial(SIP/sip_trunk_outbound/44${EXTEN:1}) In the absence of that important little stanza, the [general] settings were applying to the ad-hoc SIP endpoint; meaning that even in spite of explicitly setting the outbound SIP codec, Asterisk was insisting to use G726. No sooner had I worked this out, than the SIP trunk provider e-mailed basically to confirm my thinking. The moral of this story: Never trust a configuration file written by someone else, no matter how close it was to working ;) -- AJS Note: Originating address only accepts e-mail from list! If replying off- list, change address to asterisk1list at earthshod dot co dot uk . -- _____________________________________________________________________ -- Bandwidth and Colocation Provided by http://www.api-digital.com -- New to Asterisk? Join us for a live introductory webinar every Thurs: http://www.asterisk.org/hello asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users