Will PokerTimer run on your phone? Look in the list below to find out, and please add some notes here if you have tested PokerTimer on a phone not in the list.
PokerTimer requires a Java enabled mobile phone (or PDA). Specifically it needs something called CLDC 1.1 and MIDP 2.0. Most phones released after 2005 should work (there is a big list here)
You need a way to transfer the application to the phone as well. For now, the only one I tested is Bluetooth, it works well (at least for Nokia, Sony-Ericsson and LG) but you need a Bluetooth enabled phone. If not, you should be able to use an USB cable, IR or Over The Air download.
(this list is very incomplete, please feel free to add to it!)