XMPP or SIP Account

Maybe this one is better: https://www.ekiga.net/index.php?page=register ?

Maybe try ostel.co for SIP.

you could be a member of trisquel and you get an xmpp account.

Any suggestions on a good company to register an XMPP account with?

Why don't you just setup your own xmpp server? I didn't try it myself yet, but I heard it's not very difficult.
A cheap single-board computer should do the job; there are a few which can be used in freedom under *certain conditions*.
Definitely the best thing for your privacy if you use free software OS and xmpp server. You're the only one you can trust.

I'd like to point out that there aren't any data retention laws in the US and most data retention is voluntary. So while a US based ISP/email provider/etc may be forced to hand over logs that exist a privacy respecting ISP/email provider/etc may not actually have any. Europe on the other hand is very risky in that regard. I'm not familiar with Switzerland and there data retention laws. The US doesn't force companies to protect your privacy either though. So a company like Google IS going to sell that data even if a company like Duck Duck Go isn't. RMS also pointed out that you should avoid conducting searches with the same provider you use for email/calendaring/etc. I suppose nobody actually thought using Google was a good idea... however did anybody thing that maybe using Duck Duck Go may be less than perfect too? While I may have more faith in one than the other I'm pretty sure there are other options out there that I'd trust as much as or more than Duck Duck Go for email/sip/xmpp. Since Duck Duck Go's main thing is search and there are few good search options I'd suggest sticking to using them for search and search only so that more barriers are created.

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I'm currently experimenting with running my own XMPP server with ejabberd on Debian. Haven't quite got it working yet but that would seem to be the most secure option, imo. Same situation as with email. (And of course, use OTR).
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