You'd be surprised how many companies still use pagers for oncall alerts. After all, they're cheap, the batteries last a long time, the coverage can often be better than a cell phone, and most importantly you won't accidentally silence your pager when you silence your cell.
The biggest reason to use pagers over SMS: pagers have a guarantee for arrival by the service provider - if the device is on at the other end it will get through. SMSes have no such guarantees.
