Does anyone have any ideas on how you'd do this?

I'm wondering if we can get the IMEI in software and implement some kind of server registration system. This would mean the app is tied to each physical handset, rather than each SIM, which may or may not be a good thing.

For this your best bet is to try to get it from the android.telephony.TelephonyManager and call getDeviceId(). It will return a String with the IMEI.

Good luck.