With ThinkTel? I haven’t done anything with them but again, it’s just SIP. Chan_SIP and Chan_PJSIP are Asterisk drivers. PJSIP, itself, is a SIP driver that has been around since 2005. To put that in context, Asterisk 1.2 was released in 2005.
If I had their settings for a SIP trunk, I could bang out a config in under a couple minutes. It’s not that hard at all.