Faxing never works as well over SIP. I've used various ATAs like Cisco, Grandstream, and Obi (Poly). They might work for a few pages, but try sending a 50-page fax with them and they usually fail. T.38 seems to only work a little better than G.711
We work with a lot of healthcare providers, and we keep them on POTS or eFax. Or we bundle a line with the Internet from the ISP.
If you have an alarm line, then good luck with any ATA.