Miley was on the Kyle and Jackie O radio show in Australia this morning. During the interview she admitted that she is not single, and will likely have her boyfriend with her when she tours Australia in late June - July.
Miley didn't mention any names, but I assume her boyfriend is her So Undercover co-star Josh Bowman.
To listen to the radio interview check out The Dirt.
UPDATE: April 5th 2011:
Miley has kept it pretty quiet, but there are tons of rumors going around that Miley has gotten back together with Liam Hemsworth.