I use an Asus DSL-AC68U which overall I find to be excellent.
Regarding the SIP stuff , it has SIP passthru - whatever that means.
Unlocked Openreach modem and Linksys is my set up.
Also beening looking at Asus AC56/68U (The dual core ones l believe) as a replacement if the linksys ever goes pop...
I still think a separate modem and router set up is a better option than a combo device.
Is Guru licquorice still front ending the Tp-link with an unlocked hg612 3b ?
I believe a separate router and modem will also allow you to change/switch off/fiddle with the router without upsetting your connection speed (Dslam continues to see the modem).
In other threads it seems I may have bought the wrong fffffflippin' thing.
I have Infinity so want to replace HH5.
I bought W8980 which is (I now find) an ADSL+ Modem router.
I know I'm off topic for this thread now so I'll flip over to the correct one.
Just a note on SIP...
I've not noticed problems using a Linksys SPA3102 sip gateway alongside my BT HH5a - it appears to work fine.
Not noticed any user setting to enable/disable any SIP ALG,
Also I've run some sip apps on laptop/tablet without difficulty
I'm using poivy as the sip provider.