Location tracking

Phones connect to the nearest cell tower, and identify themselves. The matching of a phone's signal to a particular phone/SIM/person is done for 2 reasons: so they can be notified in the event of a call, or other incoming connection request, and for billing (only paying customers can use the service).

In short: if your phone is on, your cell network phone provider knows where it is.

Unfortunately, you can't just choose some network provider you trust: there are very few choices, and making new providers is inefficient and impractical. However, we can design a system where you don't provide them with nearly as much information.

First, consider a very common case: you have network access through some means other than the cell network. In this case, you should be able to shut down the cell radio, and use the other network (such as Wifi). Assuming basic privacy practices (or using a network you trust) you can get decent privacy this way. A simple approach would to to just start up a Tor hidden service, and wait to get notified over it for incoming calls. Texts and other small non latency sensitive data could be delivered directly that way. Connection requests for calls could be sent over the secured channel, and the end user could decide to open a direct (less private, but lower latency) connection. They would of course still want to encrypt that, but it could still reveal your location should you accept calls in that manner.

A similar approach can be used to use ephemeral IDs when connecting to cell phone towers (or even untrusted ISPs in general). When you connect, you provide a request which they can forward to a third party you specify in the request. This will be encrypted, and will ID you with your chosen third party, which will be billed for your connection, and in return will bill you for the data use. When someone wishes to contact you, they can send a request to said third party, which can record and forward their message, reject it, report you as unavailable etc. In the case of something like a phone call, they would forward the caller's information to the ISP currently providing your connection along with your current ephemeral ID. If you decide to accept the request, you can open a direct connection (with the privacy implications involved), reject it, or opt to open a proxied connection through said third party, which would provide an extra layer of encryption and destination hiding.

You could get new ephemeral IDs as frequently as desired, and perhaps even have multiple ones at once. This wont hide the location from which you connect, but it will help disassociate you from it.

The idea basically resembles dynamic DNS. You get a record published for how to find a service that will location you (The IP for your DNS server /third part ID system), and it can respond in a variety of ways, either directing traffic to you, through a proxy, to a offline responder/mailbox/voicemail or providing some error message. You then periodically check in with the server and update it on what to do with incoming requests. In the case or working with Cell providers and other ISPs, there may also be some billing implications that the server handles on your behalf and forwards later if appropriate).

If desired, there could be multiple levels of these services, which would basically amount to Tor hidden services.