Standard physical tactile buttons on smart phones are the lock and volume buttons. That's pretty much it. Manufacturers have differing views on what other physical buttons are included. Let's look at some of these:
Home, Menu, Back, and Search
The latest android smart phones have the infamous 4 capacitive buttons at the bottom of their display: Home, Menu, Back, and Search. Some phones (e.g., Motorola Droid X2) have opted for tactile, physical buttons for these useful functions. My question: What is desired? Do you like the capacitive (touch only) buttons, or do you have an inner desire to press down a physical button? Do you have accidental presses of said buttons?
This also begs the debate between a capacitive, on-screen keyboard (iPhone) vs a physical keyboard (Samsung Epic 4G). Could you live without your physical button QWERTY? Is the physical keyboard worth the extra girth in your pocket?
In my opinion, fighting games like Street Fighter are horrendous on a touchscreen. Accidental presses are inevitable, and intentional presses are misinterpreted. The player has to constantly look to see what they are pressing, like a 4 year old learning to play with a Nintendo controller for the first time. Turn-based, tap, and slow-paced games are great for touch-screen since the player doesn't need to constantly check where their fingers are.
What applications on a phone do you think physical buttons are a must have?