To expand on this, does anyone know of a reliable service provider (accepting bitcoins is a bonus) for SIP Trunking[0]? Or any VoIP workflow that can perform calls to PSTN[1] (the regular landline/mobile telephone network). Or even any VoIP provider that offers a basic answering service, where the voice mail box can be checked over the internet a la google voice/skype voicemail?
Don’t have any recommendations here, just thought I’d mention that for the stated purpose—preventing the tracking of the cellphone location (i.e. where you go)—running your own VoIP to PSTN/ISDN/GSM bridge at home would be sufficient.
Completely anonymous hosted PSTN bridge would be very open to abuse, so I imagine not many of them are/will remain accessible via Tor. But for completely secure and/or anonymous communication you don’t need or want PSTN, all you need is (encrypted) VoIP–VoIP that you control, and can optionally expose via Tor (as a hidden service).
Bonus points: GSM bridge at home raises less flags. You could even “take it for a walk” from time to time to make it appear even less suspicious.
2) Access Internet (and VOIP) only via VPN or better yet TOR.
3) Only give out your VOIP number. No one must know your direct number, it’s only for emergencies.
This severs all the important connections to make any use of that data, assuming you don’t have any leaks.