RPi doesn't allow you to use your own bootloader. You cannot even start it without closed blob, so it's in contradiction to your previous requirements.
I have yet to find a device that meets all my requirements (some of which I did not mention).
In RPI's favor I will say that 1. it is not "in development" but is "on sale" and 2. it does not come with Linux preinstalled. Letting users choose their own OS and not limiting the choices is a start in the right direction. There is of course further to go. Alas, it does not stop at the bootloader.
So, where do you recommend purchasing the device(s) you mentioned when they eventually go on sale?
Neo900 probably won't come with any OS preinstalled, maybe except some Debian based BSP which you'll be encouraged to replace with OS of your choice, as it won't be supposed to be actively used - it will be there for easy testing if all hardware works as it should.
It is a small project with very small target audience (currently about 350), so it won't be built to shelf, as there's simply not enough money to do that; therefore if you eventually want it you should express your interest now by donating at least 100 EUR, so you'll be counted on component sourcing. Donation will act as a rebate on the price of the device when it's out (in few months).
More details: http://neo900.org/#donate
Where to buy? Straight from its manufacturer, of course.
There's also GTA04 - http://gta04.org/ - which is already out for few years, but now it's unfortunately hardly obtainable and it seems like there's not enough interest from customers to do next production batch (well, most of potential customers probably were stolen by Neo900 :P). Neo900 is based on GTA04 and produced by the same company.
And of course there's also old good Openmoko Neo Freerunner, which despite of being massively underpowered, meets all requirements you mentioned. It should be still available at some retailers, like Golden Delicious Computers, Pulster or IDA Systems.
Also, you might want to look at MIPS-based Qi-Hardware Ben NanoNote. It's not a phone, but it also meets your requirements and it's available (though supplies seem to be near end, so you better hurry if you decide that you want it. AFAIK Pulster and IDA Systems still have it, but you can count remaining units with hand). I don't know if someone launched any BSD on it, but I can't see why it shouldn't be possible.
So, to make it clear, every device I mentioned so far in all my comments, except Neo900, already went on sale. With Neo900 it's a matter of few months.
From future devices also worth noting, there's DragonBox Pyra, an OpenPandora successor, which will also provide optional modem (the same like in Neo900 btw - those two are actually sister projects, sharing some developers).
The only thing Raspberry Pi is better than any of those devices is price, but when you'll count money and time spent on making Raspberry Pi an acceptable option when operating on battery, this probably won't be true anymore.
