Well I can tell you that any SIP program can do this, one that comes to mind is Linphone. But you do need a provider. Almost all providers deal with UDP. You might be able to find one that transmits over tcp but that’ll be a very small list. TCP isn’t reliable for VoIP, for media anyway. At best you’ll find one that encrypts the signaling over TLS, which is TCP. But audio, even if encrypted too, is done over UDP.... Source: over 1 year ago

Does Linphone (https://linphone.org/) not meet that need of cross platform (website claims versions for all major OS'es) and open source (https://gitlab.linphone.org/BC/public/linphone-desktop)? - Source: Hacker News / over 1 year ago

Similarly, you can use any SIP (VoIP) provider (e.g. VOIPo Cloud), and configure the SIP account details in your native phone app. This way you will also be able to use a SIP softphone on your computer (e.g. LinPhone on Linux or Telephone on Mac), or even a real SIP phone in your home. Depending on your SIP plan you may or may not be able to make international calls this way. Source: over 2 years ago

I heard on RFD Fonus is using linphone.org to code their service. Source: almost 3 years ago

If you are willing to "loosen" your requirements slightly, VOIP.ms (https://voip.ms/) VOIP phone numbers support SMS send/receive (including a web interface in your account to do send/receive) and using one to send/receive SMS codes would be relatively inexpensive (if you pick their "pay for usage" version). This page shows their pricing in various countries... - Source: Hacker News / 5 months ago

It appears that the ATA is not sending any traffic out when I dial. The packet capture only saw packets to/from voip.ms when I made an inbound call. Outbound, nothing happened. Source: 6 months ago

It's connected to voip.ms. The CDR in the ATA just shows that the outbound call failed. VoIP.ms CDR aren't registering that I've attempted to make an outbound call. Source: 6 months ago

Hello, I hope this is not too off-topic, but I suspect there must be many people here who have run into this. I use voip.ms, and have always received voicemails as email attachments with no problem. Since switching to Windows 11 from Windows 10, I can no longer play the files, but have to download them. Windows 11, Chrome, gmail. Error message: 'there was a problem playing this audio file'. Has anyone found a... Source: 6 months ago

This is usually very limited. For instance, I used voip.ms, and they limit it to 100 per day and costs me abotu a penny a message (separate charges for inbound and outbound, so 2 cents to receive a message and then forward it along) This is done because SMS forwarding looks spammy and the receiving carrier will block the sending carrier entirely (this is why Google had to end it). Source: 6 months ago