Openmoko Neo Freerunner (GTA02), Nokia N900 (afaik) though not recent phones. Then there is GTA04 by Goldelico.

There is also a project called Neo900 which aims to do small upgrades to N900 and fence in baseband even more. You will be in control of application CPU and able to monitor baseband activities.

Couldn't tell you nowadays. IIRC Apple still separates baseband and main CPU. The last ones I recall that did this were Palm devices (potentially up to the WebOS ones).

GSM Arena doesn't appear to have this information. You might have to go through iFixit teardowns. It's also possible this isn't something happening today -- I've been out of this arena for some time.

What you want to look for is something like this, where you see both a CPU and a processor like the MDM6600:

https://www.ifixit.com/Teardown/Motorola+Droid+Bionic+Teardo...

Practically all phones have separate application/baseband processors, since the baseband processing has hard realtime constraints; I think what you're more interested in is whether the baseband CPU has direct access to the main memory and CPU, and that's not something that can be discerned physically. Even with physically separate baseband/AP CPUs, the former might have DMA access to main memory.

Off-topic, but I couldn't help pointing out that saying "DMA access to main memory" is even worse than the classic "ATM machine" or "PIN number."

Since we're nitpicking, no it isn't. DMA is a particular method of accessing memory. You can have direct mapped access, cache mediated, PIO, DMA, etc. There can be many different memories, such as expansion cards, where you could DMA to/from, apart from main memory.

Supposedly the Galaxy Nexus has the baseband separate and communicates over a serial connection. An anonymous person passed this info to the Replicant project. I wish there was a way to verify this.