[UnLimiTeD]

So, to sum it up, there's multiple Options:

A) Your Persona is tied to your SIN. This allows you to find someone who stole your car with Comlink, though identity theft could be a problem. 
No Idea why GOD gets none of that info, though. It might explain why adspam due to various Qualities can't be removed by switching devices.

B) Your Comlink is inherent to you, maybe due to biological setup or some sort of magic. This allows the same advantages and raises more or less the same Questions as A, though there's the question where that data come from when using DNI, ad it raises an even bigger question about GOD. Also, it might allow Identity theft just by hacking the device your persona is on, theoretically. It would be interesting how that interacts with technomancers with and without device, since their points of access are so different.

C) It is based on your device, and thus you could have multiple. This is the only way a throwaway burner comlink makes any real sense, but if someone stole your car and your comlink, you'd have to go through more work to get them back.

Currently B seems to be the favourite for reasons unknown, which is kind the problem about B as a whole.

[Marcus Gideon]

Option A and C are not options supported by any of the rules in the book. That's the dilemma.

(A) would be a good idea for a house rule, justifying people having a SIN of some kind, and Deckers having multiple fake SINs.

(C) would be a reason to justify burner Commlinks, but I think they're somewhat useful anyway. When you have Marks on a Persona, you really have Marks on the device they're using. When you get 2 Marks on an Icon (the digital representation of a device) then you can use Trace Icon to find the physical location of the device itself.

Now, SR4 had rules for Proxies, whereby you could run your Matrix traffic from one device, to another, to another, before you finally hit the target. When they traced it back, they had to deal with those hops before they found your real hiding spot. It's like the movies, when they say "The call is coming from New York... No, wait they're in Los Angeles... No, now they're in London?" So you could strategically place burner Comms all over town, bouncing your traffic in circles around the city and making the cops chase their own tails before they find you.

SR5 doesn't do anything like that (yet), although it's somewhat implied by the Sneak program. But one thing you could do is get online via AR with your burner Comm in the middle of the mall. Then when you get Traced, leave the Comm turned on and toss it in the nearest trash can. While you're walking out the door to the parking lot, cops are pushing past so they can get inside. They get to the food court and find a 100¥ Comm in the garbage, and no evil hacker in sight.

(B) is the only option supported by the rules as written. Somehow, no matter what device you use, it's always the same Persona. It may not look the same depending on whether you've customized or if you stick to the default appearance for the device you use. But it's the same Persona that all your devices recognize as Owner. And yet, while all your devices recognize you, GOD has no way of telling that you are the same hacker they almost Converged on 5 minutes ago, before you rebooted and wiped your OS counter clean.

[Herr Brackhaus]

Regarding proxies. Enter a host, then make the call. Voila. You can still communicate in and out of hosts, but you can no longer be traced.

Hosts, Page 246:

The virtual space inside a host is separate from the outside grid. When you’re outside of a host, you can’t interact directly with icons inside it, although you can still send messages, make commcalls, and that sort of thing. Once you’re inside, you can see and interact with icons inside the host, but not outside (with the same caveat for messages, calls, etc.).

Trace Icon, page 243:

This doesn’t work on hosts because they generally have no physical location, or IC programs because they are confined to their hosts.

[CitizenJoe]

Maybe some of this can be resolved by what you can do to a persona.  Can you damage it in cyber combat?

[Herr Brackhaus]

CitizenJoe
Only if you're a technomancer.

Page 228, Matrix Damage

Matrix damage is always resisted with Device Rating + Firewall. When a persona is hit for damage, the device it is running on takes that damage (except technomancers, who take it as Stun damage).

[CitizenJoe]

Ok, that creates some issues.  When you bring another device under your control, it gets absorbed into your persona. I.e. the device stops displaying as its own icon and becomes a part of your icon.  You could log in from multiple commlinks (or toasters for that matter), so how does the damage get assessed? Do all connected devices take damage?  Does it get divided amongst the devices? 

[Herr Brackhaus]

You can only be logged on (i.e. have your persona formed on) a single device at a time.

Page 235

Personas are the “people” of the Matrix. Some personas are actually people, users and hackers who are connected to and using the Matrix. When a person uses a device to connect to the Matrix, the device’s icon is subsumed by the persona’s icon, so it’s basically gone from the Matrix until the persona jacks out. You can only run one persona at a time; switching requires you to reboot both the device you’re currently on and the device to which you want to shift your persona.

[Whiskeyjack]

The device you form your persona on takes damage. The commlink or the deck.

The complication you refer to would be if you have multiple commlinks. But jo matter how many commlinks are in your PAN, only one of them is "forming a persona" at any given time.

It's also notable that you can do a lot in the Matrix without having an active persona (as you can slave devices and such to your deck and they appear solely as device icons but the master slave connections are removed when you form a persona on the deck). I want to say the persona as a concept is only relevant if you're in VR? In that regard it would work like an astral form.

[Herr Brackhaus]

Whiskeyjack
You still form a persona on a device to use AR, nothing in the books suggest otherwise. Note how the quote from page 235 talks about using "a device to connect to the Matrix". It doesn't specify AR or VR, but simply talks about using the Matrix. User Modes on page 229 and 230 deals with AR vs VR, and that whole section starts with the following: "When you interact with the Matrix, you can do it in one of three modes."

[UnLimiTeD]

Well, so let's assume a SINless kid from the Barrens gets his hands on two pristine Metalinks in their factory packing, and it turns them both on at the same time. What happens?

[Rooks]

Generalist analogy two things are needed to access internet/matrix a MAC address (think VIN or device serial number) and IP address (or licence plate number) one is inherently tied to the device (vehicle) used another is assigned based on the system (license plate) when one reboots their device the will get another ip address (a new license plate) you will generally not broadcast your MAC address but you could potentially broadcast your ip address (license plate/commcode) so when you are legally surfing the internet/matrix people think you are a legitimate user its only when you dont want to be found out (run silently) that you are driving without lights or a license plate on your device/car

[Rooks]

Well, so let's assume a SINless kid from the Barrens gets his hands on two pristine Metalinks in their factory packing, and it turns them both on at the same time. What happens?

it asks for owner identification default setting is whatever company made them and they need to go to an authorized or illegal retailer to activate it under a new ownership (which is why you generally buy from your deckmeister arms dealer fixer) as they already scrub/filed off the serial numbers so to speak

[Herr Brackhaus]

Well, so let's assume a SINless kid from the Barrens gets his hands on two pristine Metalinks in their factory packing, and it turns them both on at the same time. What happens?

In terms of the core rules; one of them forms the kids persona, and the other just boots up.

ETA:
Rooks does have a point; assuming they were in original packaging they wouldn't have an owner, so you'd need to change ownership of the device first.

[Marcus Gideon]

A few things...

Personas are a type of Icon, which is a digital representation of a user logged into a device (unless you're a TM in which case it's a digital manifestation of your grey matter). When you damage a Persona, you're really damaging the device they're running on.

If you simply power up a device, it appears on the Matrix with its own Device Icon. Only when you start actively using it for things, does the Device Icon get replaced by the Persona Icon. And in a case like this where you're talking about someone just letting both Commlinks take incoming calls, there's no reason for there to be a Persona involved.

[CitizenJoe]

It says you can only have one active persona at a time.  It doesn't say you can't have multiple devices accessing it at the same time.  In fact it specifically absorbs other devices into the persona.