I've not tried this myself, but it seems that the best solution is to create a Bonjour based server that the iPhone client can discover. This is apparently what the Clink Task app from ClinkApp.com does.
The code for doing this was demo'd in Cocoa for Scientists (Part XXVIII): Bonjour and How Do You Do? - a tutorial on the MacResearch website.
Its pretty simple to set up the communication channel. The "hard part" will be doing the sending/receiving of data. The writer covers that in a subsequent tutorial and there are probably some frameworks out there you can make use of.
See
Cocoa for Scientists (Part XXVIII): Bonjour and How Do You Do? | MacResearch