Phone plans for the last few years have had different data quotas for tethering & phone apps, but lions have always envisioned a phone app which forwarded packets from ADB or some proprietary USB protocol.  The confuser side relies on user space networking with the tun/tap driver.  The easy phone app tunnels the packets to a server on a wired network, but lions normally only need tethering because they don't have a server on a wired network.  

The hard phone app strips all the headers from the packets & forwards the payloads using android networking calls.  Lions have been writing low level networking code for so long, it might not be as hard as it would have been 20 years ago.  Obviously, no app store would be allowed to distribute such a program & no-one among the current generation is interested in circumventing the system.

The idea got a bit more motivation in the last 2 years because labor shortages have made Comca$t less reliable.  It's become more important to have redundant ISP's.

--------------------------------------------------------------------------------------------------

9/2025:

Revisiting this problem after 4 years.  The TTL hack hasn't worked for years. They use a dedicated paid rmnet device for all tethering now.  A fully paid tethering plan is still pretty unreliable compared to phone apps.  They might be giving the tethering device a lower priority.

  It's kind of languished because the phone company obviously would already have plugged up every possible hole.

The need for tethering has shifted from daily commuting to the continued problems with the lion kingdom's Comca$t gateway.  There is a free solution which is to only use xfinitywifi, but certain apps don't work with it.  The leading candidate is a phone app that provides user space ppp over USB.

The journey begins with sending bytes over a raw USB device between a PC & a phone app.  The phone basically only presents ADB & some managed functions when it's a device.  Plug a serial dongle or custom gadget into the phone & it can theoretically do anything over USB as a host.  You'd want the PC to appear as a very fast serial dongle. 

---------------------------------------------------------------------------------------------------

11/2025:

Further review of the problem revealed it would need to create a virtual ethernet device on the phone for any kind of transparent packet mangling.  Helas, this is not possible on a cheap phone.  Instead, the phone app would have to replicate every TCP connection from scratch, manetaining a table of connections to forward the data to.  Helas, UDP port listening would be quite difficult.  It would need a user supplied table of ports to forward, but this is commonly done for virtual machines.  It basically has to do everything a virtual machine does.

The lion kingdom since discovered its phones all supported 5Ghz wifi since 2025 & this was much faster than any other method.   The game would be to have the phone on an offline 5Ghz access point while using its own data for internet.