You can sell your products by Handango. Here an example:
For the signature, I'm not sure if you are forced to sign it before you sell it, and the applications are suppose to be able to run on the phone, even unsigned. But I know on the last Sendo OS, we were force to use the sendo signature. Right now, this market is really complicated and a lot of things are unsure...
I think you will be forced to deal with them :(
For us, all our games were signed by orange themself.
I hope this post help you a little bit, but I don't know much either.