This thread is confusing. The topic was initially about how the Transcendent Grid Complex Form works, but now it's about commlinks?
The Transcendent Grid thing is simple enough: you're connected to all grids at once. Instead of segregated Grids, they're essentially all one Grid.
Also, the OP was asking about what grid the technomancer was on to begin with. The answer is this: it depends on your lifestyle. If you're at low or less, you are on the Public Grid, which is crap to begin with. If you're at medium, you are on a city, local, or region grid (like the Emerald City grid in Seattle). If you're at high or above, you're on one of the megacorp grids.
As stated earlier, having access isn't the same as being registered. We actually don't have a clue how the Grids register users. The Trace Icon action can trace a location regardless of the Grid the icon is running on. We don't have rules for how to use Trace Icon after the icon has gone offline either - so the answer gets complicated.
As to the secondary topic of a technomancer using a commlink - you can't use the commlink to spoof your location or grid while still using any Resonance abilities (including Complex Forms). The only way that the commlink would spoof your location would be if you ran your persona through it. And that's not going to work well for a technomancer. Even without the Resonance action issue, a commlink lacks the Attack and Sleaze attributes, so you'd be useless for hacking.
You can run a commlink to broadcast your SIN, manage your PAN, etc. as a technomancer just fine. Your Living Persona doesn't actually have to be active until you want it to be active. You're not running around involuntarily broadcasting a signal - you're in control of it. 4th edition had rules for handling a technomancer that stays hidden for extended periods of time, but with the changes to the Matrix I'd be surprised if those rules made it back into 5th edition.
