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Applications section is on top right side when you click xx's iphone
MediaBurner dont need  to login, it should not be prompted by MediaBurner, can you upload a screenshot ?
Connect your iPhone to computer, launch iTunes , locate to xx's iPhone > Applications
Find and click MediaBurner, all the shared videos are list on the right side.
m4a format, you can rename to m4r and import to device as ringtone
iTunes > xx's iPhone > Applications > MediaBurner
m4a format, you can rename to m4r and import to device as ringtone

Can you send me the video link? I will try to find what makes error.
Yes, playlist is planned. it will come soon
Thanks for your report , it will be fixed next version
The audio item is list on Download list with prefix "[audio]" just select one and "Share in iTunes" , then connect your device to computer, launch iTunes, locate to Applications , find and click MediaBurner, you can see the audio is list there.