Not sure if you are always leaving the same call back number on the pager (didn't know those were still around) but if so you might try entering the whole number in your address book.1. Hit the home button to wake it up.
2. Slide the slide to unlock it.
3. Hit the phone icon (or if I left off in Safari or something first I have to hit the home button again to get back home so I can hit the phone icon)
4. The phone dialer comes up and this is certainly much faster and more user-friendly than any cell phone keys... however...
5. Once the pager number answers I have to hit the "keypad" button to get to the keypad"
6. Enter the number I want to be called back on.
In reality I've "touched" the phone many more times than I would touch my $49 Nokia to make the same call. But it's lots more fun.
I did this with my bank's automated system so I didn't have to type any numbers to log in. When setting up the number pressing the +*# key will show a keypad with "Pause" on it. Insert as needed. Only problem is that the tones it sends are very long.