I've just had a stack of calls from different numbers constantly for 30 mins straight:
(02) 6190 7641
(02) 9157 2800
(02) 9157 6328
(03) 7065 8851
(03) 7065 8866
(03) 7065 8885
(03) 7065 8889
(03) 7065 8890
(03) 7065 8899
(03) 9969 6415
(07) 3187 8513

They all seem to be fax calls, all have left a VM of varying lengths (up to 5 mins long) which are just beeping noises at ~3 sec intervals.