What kind of hardware can be used to speed up the writing on android phones?
I realise that this isn't an answer to your hardware requirement, but are you sure you need new hardware?

I believe that the current Guinness World Record speed texting record holder used the Swype keyboard on an Android phone, so it's not exactly slow.

Swype is pre-installed on a number of Android phones (primarily Samsung models) but unfortunately is otherwise in a limited beta that you'll need to register for. There are some similar soft keyboards like SlideIt that are available in the Market