Texting on the iPhone 4 clumsy and inaccurate.  When I received the iPhone 4 the first thing I did was seek out a swipe text app, and as of the date of posting this swipe text apps do not exist for iPhone 4. 

The best thing I've found to increase the speed of texting on the iPhone 4 is to turn the phone sideways so that the keyboard uses more of the real estate on the touch screen.  This avoids fat finger errors, which I find to be the most common problem while texting.   Because the iPhone 4 is a touch screen there is no tactile memory of where each key lives.  You will not pick up speed as you use the phone more frequently.  There is no "learning curve" for texting on the iPhone 4.  It will be painful the first day you use the phone to send text messages and will likely not become any more efficient for you as time passes. 

Also please note, do not attempt to text and drive on an iPhone 4.  In comparison to the Blackberry, which was fairly easy to use while driving, the iPhone 4 is the most dangerous phone I've used to this point in terms of texting while driving or answering phone calls while driving because each operation requires the users to focus their eyes away from the road and on to the touch screen.

There are currently no future plans from Apple to implement swipe texting on future iPhone releases.  iPhone 5 will have a larger screen than the iPhone 4 which will help to eliminate fat finger texting errors that the iPhone 4 is prone to.

Swype has plans to deliver a swype-texting app for the iPhone but it is not known if Apple will approve it for use. 

Begin your iOS evaluation now.