Just purchased iTunes Match and wasn't sure about 2 things. Does it erase all the music from my iphone if I turn it on? If I loose wifi can I still access my music? Thanks :)
Yes. All the contents on your device will be replaced with your iTunes Match libary and you will not be able to access it without connection to the internet.
Turning Match on does not erase your music, it adds to it by allowing non-iTunes purchases to move through iCloud. You need some form of connection, whether WiFi or cellular data to access what is not on your iDevice and in iCloud.
Read through the knowledge base article on iTunes Match subscription.
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