How does a carrier-locked phone know it's locked?

[Gorf123]

Just trying to help someone on another forum.

My understanding of "locked" handsets is that, broadly speaking, if they show the carrier logo during boot then they are likely to be locked to that carrier. If they show the manufacturer logo during boot, they aren't locked to a carrier.

A couple of years ago, I rooted my HTC Desire and put CyanogenMod on it. At the end of my minimum term, I gave it to my son and he's been using it for the last year on a different UK carrier, without unlocking. The thing is, before I put CM on it, I was getting the Virgin ident during boot.

This means that either the phone wasn't locked to Virgin, meaning that what I've said in the second paragraph is wrong, or that putting a new ROM on the phone has also unlocked it.

Can any experts shed any light on this? I thought that phone locking (to a carrier) must be pretty low-level, below the phone's operating system, because it needs the IMEI and a dialled code to unlock it...

 

[BRAINZ2013]

They may have had used cyanogenmod cause its universal with a edit to the build.prop you can use the device . if they flashed a gsm patch that has to be also altered with radiocomm software. This software sends a command to change the ril to show that the device has been unlocked now when you flash the patch it just edit the nvo files. But it depends on the device .

 

[Hadron]

The rooting method you used (from checking your post history) would not have network-unlocked a Desire. Nor would installing CM on it. There is a software unlock for the Desire, but you would know if you'd run that. So my best guess is that yours just wasn't locked in the first place.

However, Virgin are a virtual mobile operator, i.e. they piggy back off one of the big networks, formerly T-Mobile, now EE. So I wonder what network he is using it on and whether this is important? I've heard of Virgin SIMs working in T-Mobile locked handsets, though I didn't think it worked the other way round.