(keitai-l) spam phone calls.

Does anyone know Docomo's attitude to what  (I think) are SPAM phone
calls? I have had 4 "1 ring" calls from an ordinary Fukuoka number that
just leaves the number. I called back once (the first time) and got a
recorded message saying "kyoumi ga nai hito..." at which point I broke the
connection. My guess is that this is SPAM - but I don't want to
investigate further in case it is expensive to do so... I suppose the
sensible thing wouold be to call from a payphone.

I have initiated the call in the legal sense, but if this is SPAM, how do
DoCoMo treat this kind of thing? Is it worth complaining?

The number is 092 451 3313 if anyone cares to investigate from a payphone.

Nick