I just had it happen to me also, i didnt recognise the number so i didnt answer and waited for a message but they didnt leave one but when i went to call back it beeped so id really like to know what is going on...

Me to, I just got a call on my mobile no message left.

Number called without leaving a message, and whenever I try to call back, I just get a beeping sound, and "Number Busy" displayed on my screen.

I answered this call and its Wheelies - support people in wheelchairs