Well, this is an idea I want to build. Yes I know it's 2013, people use media files (CD, DVD, memory stick, etc.) instead of the old FM radio, but you don't know where when it will come handy to have one.

So here is the basic idea:

I saw this on a DIY website and I thought, why not take this to another level?



This is USB so it would work with the N900 USB host for power, but not many phones can do that, so we need a self-powered FM transmitter. Also cables may get in the way, and the best method to replace cables is AD2P since every phone have it.

Now at this step we're going to get something like this:



This is a AD2P receiver with a 5V 140mah battery.

Now we open this up and get power for the stick above, then hook up the input of the stick to the output of the receiver, bound them together and you have your own wireless FM transmitter for any device with AD2P ready.

Now, the problem is that the USB transmitter above is very basic, it just broadcasts and you can't select frequency, and you need that so that's why I found this:



Now if we want a clean work we should search for more specific hardware:

And here is a Micro-USB powered FM transmitter:



and this Micro-USB AD2P receiver with keys:



And now they are just stand-alone, but if we're working with packs, even when charging we should use a pack, so we are going to hook the power trough a cable like this:



And here you have your own wireless FM transmitter.

I hope you will enjoy this!