How can mobiles always make emergency calls...

[Myriad2112]

... if there is no line or signal?

[RATTER15]

It just means that for emergency services they are able to lock on to "any" network, giving a far greater chance of receiving a signal

[RATTER15]

I think!!!

[ChuckFickens]

Close....

It's nothing to do with the Emergency services though.

Any phone can work with any network, it's only the SIM card that determines which network the phone uses, emergency calls are allowed to use any network.

So although (for example) you may not have a signal to O2 if you need to make an emergency call your phone would simply use the strongest available network to make it.

[ChuckFickens]

And before anyone mentions locked phones, they can still use any network, it's just a restriction in the software of the phone that tells it not to use another network and emergency calls are not included in that restriction.

[RATTER15]

Just what I said, without the detail! :-)

[Duncer]

I believe 112 works as an emergency call.