[1Old Pro]

Pagers are used by any number of people who have to be able to be reached no matter what. Cell phones are mostly reliable. Key word being "mostly". But the reason doctors on call carry pagers is because they are far more reliable.

Pagers use radio signals that are stronger than cell signals so they are useful in an area with less technological investment in towers. Secondly, the reason drug dealers and terrorists like them is that you call back using a land line which is less susceptible to being intercepted.

[Harmless Teddy Bear]

Or just using someone else phone. Or a burner that you promptly stick in someone else pocket or toss in the back of a truck passing by.