Personally, I am not too big fan of iPhone, especially regarding earlier versions.
Than again, as a honest technology geek, I also must admit that iPhone 3GS set high standards both in arena of mobile devices as well as in arena of PDA and general mobile platforms; operating system is way better, development support (SDK, tools) gives you opportunity to create stunning applications, and on top of that, iPhone store can give necessary head start and much needed customer and community support.
Beautifully crafted, both from technical and design side, small, fast and (on top of everything else) very useful – Run Mate is real example how one mobile application should look like: it should follow all the standards of the underlying ecosystem (operating system), giving to end user maximum benefit for really, really affordable price.
If you are into any kind of walk recreation – running, jogging or just walk in different paces – this is the right application for you. Head to iPhone store, and follow updates on @runmate at Twitter; for any other details / support, here is main site: http://codeaplus.com/runmate/