Wanna talk about that? (specifics of Eastern hemisphere apply, mostly GSM or 3G phones)
Discussion
I would love to but I'm not really the smartest when it comes to phone networks. I know a phone's IMEI is a pretty sure fire way of identifying a phone and without it you can't really access cell networks because I've broken enough phone operating systems by nuking that number accidentally.
Being able to edit it while your phone is off would be pretty incredible.
It depends on the network, actually. Where I live, over around 15000 phones with zeroed-out IMEIs are estimated to circulate in the networks and no one (almost) gives a damn. It's the combination of IMEI + IMSI, not IMEI alone, that identifies the phone.
Some other countries explicitly block zeroed-out IMEIs, I know that too.
What is the cheapest non-Nokia featurephone you can get now? Chances are, it might have an IMEI editor built-in.