The best replacement for udid is imei.

The best alternatives to udid are rated as following:
★★★★★  imei
★★★★★  iccid
★★★★  idfa
★★★  uuid iphone
★★  mac address
★★  meid
★  device token
★  uuid
★  serial number
  udid

Your alternative for udid is not listed? Suggest!
Speaking about udid, one probably shouldn't forget about ios.

Other search terms related to udid and their ratings are:
★★★★★ ios
You have in mind a companion for udid and it is not yet here? Propose!



Google Trends

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udid
imei
iccid