Mac: If you prefer to use a keyboard to type on your phone or tablet but don't want to actually buy one, Type2Phone will allow you to use your Mac instead.
If you've got an iDevice running iOS 3.2 or higher, you can use external Bluetooth keyboards to type. Type2Phone is an app that makes your Mac appear like a keyboard to your device so you can use it to type rather than tap. This is really handy for responding to text messages at work, for example. You just have to make sure your Mac's Bluetooth is on and your machine is set to Discoverable. Once you do that you should be able to add it from your device without issue and start typing within a few seconds.
Type2Phone will run you $5.49, which is a little high for a single function. That said, since it saves you the cost of buying a Bluetooth keyboard, it's not entirely unreasonable.
Type2Phone ($5.49) [Mac App Store]