The one thing I wish I knew about unlocking my Android phone

For some reason I decided to unlock my HTC One X phone. I believe it was because your phone comes bundled with a fixed set of applications that you can't remove. These take up about three screens, and result in paging through trying to find the useful ones you actually installed. You do this by going through several steps, one of which is visiting www.htcdev.com and getting a code.

But what you probably don't realise, as I didn't, is that this clears your device's cid code. Your cid code is what defines the operator who provide you with updates. When you apply an update, the update has a cid check embedded in it, and will error helpfully leaving a red triangle surrounding an exclamation mark on a black screen.

Once you have cleared your cid code, there is not way of setting it again. Not for an HTC One X device at least. The reason for this is that there is apparently something called S-ON and S-OFF, and if your device is S-ON then you cannot alter things like the cid code. HTC choose not to allow toggling this off for the One X. If you can toggle it off, it is apparently easy to set it again with a fastboot command.

TL;DR: Don't unlock your HTC Android device unless you know you can set it to S-OFF. Otherwise, you won't be able to apply the updates you download from whatever telecom company provides them.