The Nexus 4 & 10 are NOT compatible with Mifare Classic tags because Mifare Classic tags do NOT adhere to the NFC Forum's Standards. They can not write to the tags nor can they read information that someone else has written to the tags. However, they can detect the UID Code (kinda like a UPC code) of a tag which is unique to every tag. So, if you use an app like NFC ReTag or NFC Task Launcher which has the ability to just detect a tag and read it's UID code, and then launch settings/profiles/etc then you can still use Mifare Classic tags with the Nexus 4 & 10. This is why some people keep saying they are compatible. Just remember, technically they are NOT compatible - the phone can just read the UID code off of the tag.