On GSM phones, ESNs don't apply. IMEIs are the equivalent, however. In that case one of the value-adds of an integrated module is that it comes with an IMEI. If

On GSM phones, ESNs don't apply. IMEIs are the equivalent, however. In that case one of the value-adds of an integrated module is that it comes with an IMEI. If you're going into large scale production you can pay CTIA for your own block of IMEIs and reprogram your modules, but typically that's not worth it. However if memory serves (it's been about 5 years) they force you into doing this if you get above a certain production volume, otherwise it becomes difficult tor track which chunk of the traffic is yours, and whether or not you're shipping a ton of devices which haven't passed carrier certification, etc. I'd imagine it works similarly with ESNs, but I have no experience there.