I will be the first to admit this is above my paygrade. But, I know when I setup one with AT&T a long time ago, when Pjsip was first put in, they kept rejecting everything being sent until I changed everything over to legacy sip. Firstcomm specifically said legacy sip on 5060 only. But, they have been useless as far as asterisk is concerned anyway - all thy could send was some old trunk config sheet from a trixbox screen shot…