TouchOSC is probably the best OSC app for the Iphone currently, however, there is also Mrmr. Mrmr is an open source program and is a little harder to configure than TouchOSC, but can do the same things. TouchOSC is also developing a configurable interface, so you can design your own. So, in my opinion, if you know what you’re doing with OSC messages, you can get away with Mrmr, but TouchOSC is a good buy.
With all OSC currently, you will still have to route the messages through Max/MSP, PD, or OSCalculator to use with Ableton 8 or Traktor Pro.