The best I have in my country (Australia) are SIP providers. They generally only offer landline numbers; I think some might offer mobile numbers but I have not tried those services (they cost more and I suspect texting won't work anyway).
Nonetheless some simple self-hosted SIP-XMPP bridge software would be amazing. We'd also need XMPP clients that understand this, however, otherwise using existing tel://xxx address books would be fiddly (you would have to manually retype them to be an XMPP address).
N.B. SIP clients on phones seem to be a bit slow and unreliable. I use one daily nonetheless, along with Snikket (conversations), which also has its fair share of issues on different people's phones.
There's one problem with this setup: emergency numbers may not work and might get routed to the wrong place.
I know the latency is already a thing with regular wireless phone network and we will probably never get back to analog wired level but it is still much lower than the latency the instant messaging apps call have, which is just too much to be bearable for anything else but the very occasional call.
I've compensated for this in IM calls by speaking with a more deliberate and measured cadence as well as adding slightly longer pauses (and waiting for such) at transitions in conversation. At least for me, it's worked just fine.
I have plenty of friends on the opposite side of the planet who I can carry a conversation with despite the latency by following this.
Edit: Calling to German landlines is $0.015 / min. That's a competitive price as such. But the monthly fee doesn't make it overly interesting for my usage pattern.
I have also looked for VoIP providers offering competitive per minute rates to European phone numbers with no monthly fee. I did not find much. VoIP seems to be somewhat popular in Germany and there is no lack of providers. But their contracts include a German phone number which I don't need and cannot even legally get because I don't live there. I don't think SIP vs XMPP would matter for me.
Not at all. Have a look at https://snikket.org for example. This let's you set up your own XMPP server that "just works" in a couple of minutes, and then you can hand out invites to your friends and family, so that they can install the Snikket app (Android or iOS) and are automatically registered and in your contacts in a few taps, without them even needing to know what XMPP is.
The server is the well-known Prosody, dockerized, the Android app is a re-skinned Conversations, the iOS client is based on Siskin IM.
And just like that you have a working, private, self-hosted, end-to-end encrypted cross-platform messaging system that also support a/v calls out of the box.
It really is pretty cool.
It is still kind of around, but it became a completely different kind of a network under its new ownership. Most channels went to libera.chat, but others went elsewhere.
Imo they needed to be stricter about what constitutes a standard XMPP server, especially with security-related stuff. Look at how browsers managed to ban old TLS versions and discourage plain HTTP.
And less important but just annoying, XML was a mistake that they keep defending. Really only made sense for rich text message body, which nowadays nobody cares about either. I've seen a project where they just shoved JSON into it and called it a day.