Modify emergency number detection

It's possible for an application to dial an emergency
number by appending extra digits to the phone number.

For example, one could dial "9111" instead of "911",
and a strict .equals wouldn't detect this as an emergency
number.

Replace .equals() with .startsWith()

Change-Id: I87f34fc2b9bbee2c4fa6be511bcc3b955559e0a9