Mobile Device ID location

iOS:

IMEI/Serial Number - to find this ID, go to Settings > General > About and scroll down, see https://support.apple.com/en-us/HT204073 for more information. Alternatively, you can dial *#06# and the ID will automatically be displayed.
UDID - every iPhone, iPod touch and iPad has a unique identifier number (UDID) associated with it, see http://www.macworld.co.uk/how-to/iphone/how-find-out-your-iphone-or-ipad-udid-3530239 for more information.

 

Android:

Device ID - the IMEI/MEID/IMSI can be found on the device's status page, press Menu > Settings > About Phone > Status. Alternatively, you can dial *#06# and the ID will automatically be displayed. See http://www.wikihow.com/Find-the-IMEI-or-MEID-Number-on-a-Mobile-Phone for more information.