This seems to be begging for a DIY project, doesn't it?

A 3d printed case, a little SoC, perhaps a Raspberry Pi Zero, as the brains with asterisk and some additional open source software providing a web interface running on it.

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hellweaver666 6 hours ago | parent [-]

Would i require some public server side component to handle the call routing etc? (or could you just use something like Google Voice?)

	▲	philips 5 hours ago \| parent [-]
		I went the DIY route (you can find the details as a parent comment). But, I had good luck with voip.ms as a SIP provider. It is inexpensive at $1.10/month for the phone number and $0.008/min for calling. And it has a pretty good history of user forums, wiki, etc for debugging hints with various hardware.