It is certain that telecom carriers participated willingly in the massive collection of telephone network CDRs from way back when these were on mag tape.
So far, every time someone has asked "What if the government is using X for surveillance?" the answer has eventually been yes. 100% of the time. Nothing is out of bounds. And that includes making partners victims if it is part of the mission to collect everything. Belgium, for example, is both a partner, somewhere in the hierarchy of partners outside of the Five Eyes, and a victim of GCHQ hacking. Being a partner doesn't spare you and being a victim isn't indicative you're not a partner.