Can a phone pretend to be a Bluetooth keyboard?
I'm surprised nobody has answered pointing out BlueputDroid as an Android solution for that. At the link you can find further information about device compatibilities.
I know this thread is rather old but I think it's worth to let it documented so others would end up here as me and will find an answer, at least for the Android half of the question.
EDIT: if you have problems to get your device connected to your ps3 like I did, try this out:http://forum.xda-developers.com/showthread.php?p=19881739#post19881739