I'm posting this here in Development because the developers usually are more interested in this kind of stuff. I'm not 100% off topic because I have a project I'm working on that controls a custom Arduino board (on PCB made like this) with the N900.

The community I'm part of has a custom PCB order that goes out every 2 weeks.
The cost it's $5 per square inch for three copies of your design. So, a 2 square inch design would cost $10, and you'll get three copies of your board. Shipping by US Mail is included, and there are no setup fees. Your boards will be mailed within 9 days of the order deadline.

Here is the link:
http://dorkbotpdx.org/wiki/pcb_order

and here are some pictures with the custom boards like they returned from the fab house:
http://www.flickr.com/photos/laen/4013181884/

Edit:
here is one of the PCB I got and I'm working on:
http://lh4.ggpht.com/_wyAZ3sieWE4/S_...100526_005.jpg

That's just PCB manufacturing though, no assembly correct? I noticed that one of your shots had a bunch of pads for some SMT components, but surely you're not planning on soldering/assembling those by hand??

I've heard BatchPCB offers the same service on a regular basis for anyone who's interested (you submit your design, and it gets added to a larger order with other peoples). I haven't actually been able to justify ordering a quantity of PCBs for projects yet, but on the bottom end of the barrel I've found that Futurelec offers some pretty darn cheap manufacturing as well.

Whoa I just read the actual website and realized it's $5/sq Inch for 3 boards! That works out to actually $1.66/sq Inch/board... that's pretty cheap

What's your arduino board do? I assume you're using some kind of bluetooth sheild to connect it to the N900?

We do SMD by hand, usually using hot plates, actually on 27th this month we have an open lab to show how to do that and you are welcome to come! I'll be there too.
Our PCB order guy is looking right now for a solution so we can get stencils too for SMD (to easy apply the soldering paste).

The Arduino board is connected to a router that runs openwrt. The N900 controls the Arduino over wifi.

What is the copper thickness for this order?

I'm not sure, you should send an email pcb-order@laen.org and the guy who actually handles the pcb order will answer you, or come to #dorkbotpdx on freenode.