I think any such device will need the 746 converting to DTMF dialling and things that do that also add # and *.
It's something I've pondered too but with my old ISP it was cheaper to have 'phone and broadband than just broadband and since changing I effectively pay for the 'phone line and get broadband free.
My PTSN line is only used for incoming calls; outgoing ones are via a VOIP service and normal calls are about a penny a minute. That also needs pulse to tone converters in the telephones.
This thread may be helpful:
https://www.vintage-radio.net/forum/...d.php?t=172549