Have you met Type2Phone?
Type2Phone does exactly what its name implies: you type (or paste) on your Mac and text appears on your iPhone / iPad.
More precisely, Type2Phone emulates a Bluetooth keyboard to which your iPhone 3GS or later can connect. iOS 3.2 required.
Start typing and your key presses are forwarded to your iPhone. Paste text and the iPhone receives the key pressed to input that text.
All this comes in handy to:
★ Type SMS text messages
★ Reply to emails on accounts mapped only on your iPhone
★ Send Tweets and update Facebook status from the office Mac
Type2Phone 1.2 supports the following keyboard layouts:
★ U.S American