I believe that most Android phones with Android version 2.1 or higher have this capability. All you need to do in order to get speech to text or anything else, for that matter, is to install the Vlingo voice app which is free from the market. It's called Vlingo Virtual Assistant. This software is exactly what is installed in the new Samsung Galaxy SII, it's just built in because Samsung and Vlingo made an agreement to have it pre-installed.
PS: The software actually does alot more than just speech to text. I use it for sending text messages, placing calls, searching for all kinds of things. I even use it sometimes to update my Facebook & Twitter statuses. I'm using it with my HTC Droid Eris and I love it.