Hi''
Ok for starters if there is going to be a new hardware model of the iPhone, chances are that the only main difference will be a larger hard drive. As it is in the states right now, the fastest cellular data network is 3g so no speed enhancements will happen.
Software version 3.0 will be released this summer adding many new features to the iPhone including MMS, stereo bluetooth, syncing notes, landscape keyboard and much more.
If you buy an iPhone now, you will be buying the latest version and it will remain that way as long as you do the 3.0 software update when it is released.
Thanks
Have a nice time ahead.