There is another texas holdem poker game called multiplayer championship poker or something like that by realdice which allows for multiplayer over the internet via edge/3g signal/wifi. This means you can play against anyone else with the game from your cell signal.
I like it because you can play not only against other iphone owners but anyone else on any other cell phone. I was playing against someone with a blackberry and a windows mobile device the other night.
The apple holdem games is tops as far as graphics is concerned but multiplayer championship poker is great for playing against real people. It also has ring games (cash game style which is a different playing style from tournament play), tournaments play, and sit and gos (single table tourneys which is different playing style from multi table tourneys). So in terms of depth and breadth, multiplayer championship poker is tops.
There is a bug in the program however where in the ring games if you are heads up against one opponent, the button is the big blind and acts last pre-flop when in fact the button should be the small blind and act first pre-flop. For any serious holdem player, this is a big deal. I informed the developer and got a response within a day that they would fix it in the next version.