Still have pagers where I work. We (developers) share one and rotate it around the team (each person has it for a week) for application support. As far as I can tell, it's better than any of the alternatives.
We have a hunt group in our phone system for on-call that forwards incoming calls to an individual based on a schedule. It can try multiple numbers and also send e-mail alerts. No SMS functionality though which is a downside.
Better than email on a mobile device?
No return on that investment. Hardly anything can be solved via e-mail. Call comes in, 99% of the time I need to log in remotely to solve it.