TUAW has a fascinating article about a TCG called Urba Rivals getting a test run on the iPhone where players can do battle using various cards, and its worked decently well outside of the iPhone environment already.
The game uses an interesting model of in-game “pack” purchases (similar to the model used for Magic: The Gathering Online) where you can purchase 1 pack of 3 cards for 99 Cents (the cost of the app), or 11 packs for $9.99
