hmm I sent a mail to Sigmatel and got THIS replay... -.-
I am sorry but we only provide datasheets to qualified customers and distributors after appropriate legal documentation is in place.
That's to be expected. Not many chip manufacturers will just hand you datasheets if you ask. Most of them won't even let you see one without signing a whacking huge NDA, which effectively renders asking for datasheets moot, since we won't be able to read them. (NDAs usually state that you have to keep the information in datasheets confidential and not share them with anyone else.)
Also, as I stated above, having no free toolchain for the SigmaTel chips is going to be a big problem. Unless you're willing to pay around $12,000, and be the only one allowed to use the kit, there's not many options we have.
However, with Freescale Semiconductor recently purchasing SigmaTel, things may change; details on that are here
if you're interested.