05-04-2020, 03:18 AM
Sipgate should work. It's been a while since I tried a software client, but it's fine with a SIP desk phone and with Asterisk. I hesitate to recommend them as they're rather backward in their encryption support. They have a bunch of different domain names covering different service levels and countries, but sipgate.com should get you started. I think they do mobile in a subset of the countries they cover.