silent.link recently added US/UK inbound voice identities.

they claim your mobile number is not known to your local mobile provider due to roaming and an adversary cannot collude with your local mobile network provider to surveil you.

they also claim they do not have the nessacary data to assist with triangulation, however, an authority could jump through several hoops if they know the IMEI (hardware identifier) alongside previous location data to continue tracking the IMSI (number identity) through a local carrier. seems fairly difficult to accomplish if i'm understanding correctly.

o'dell had them on a citadel dispatch episode recently. you may have already listened. he begins discussing the triangulation topic around ~21 minutes. https://bitcointv.com/w/qnFErBK86d6XKzNXzbXfda

obviously not a perfect solution. it does appear to be one of the better options currently. they seem based and working in the right direction.