Phones have many uses. I'd rather have my phone with me to call in an emergency than try and find a pay phone or landline that worked.
They also have their uses during incidents.
If we didn't have phones it might prevent people taking photos and videos which can be used in investigations as a means of evidence (like CCTV footage) in incidents.
I remember previously there being at least one incident of people giving useful intelligence to security by phone while an incident was in progress, for example, things like how many perpetrators, hostages, where they are, how armed they are etc...
The use of phones can be traced and assist in other suspects being traced and provide further evidence.
I'm sure family and friends are glad for being able to know a loved one is safe quickly, post it on Facebook via your phone or use the incident check in and you can reassure a lot if people very quickly. I was relieved to have this after the attacks in Paris and Brussels.
Also can be used for a warning to keep away from dangerous areas or to get help.
All sorts of benefits from the technology we have today.
(Sent from my iPhone)