It is the San Diego 911 dispatch office. I called 911 about a problem and then accidentally called again and they called me from this number to confirm that there was no problem.

I called the SD sheriff dept and they confirmed that they did make a phone call to me.   They told me their number should be unlisted but somehow my called id showed the 858-565-9559.  In any case, after checking - I "think" it was a valid phone call from the SD sheriff.

FYI: SD Sheriff phone line is 858-565-5200

This person called me on my cell phone twice today. Who are they?

This number called twice last night, the second time I picked it up.  It was the non-emergency hotline from the SD Sheriff.  They called to investigate a 911 call they received from a cell phone.  Since they can't locate a cell 911 call like they can a land-line 911 call, they use a database of phone number associated with the number that initiated the 911 call.  I was not sure if they were for real, so I asked for a callback number.  They gave me their number (858) 565-5200 and an "event" number.  They are for real.  It's the Sheriff Dept calling from this number and what ever they are calling about is not a hoax.

got a call from this number and so i called back but its disconnected...weird!

I did not dial 911 five times as this person who called back on this number said I did.  They left 5 messages claiming to be 911.  I called my cell provider and they blocked the number.  Really weird!

On 03/05/10 the number was used by 911 to try to confirm a silent alarm at my home.  However, we did not set off the alarm, the response by the police was very suspect.  They woke up my family and searched my home at 1am without my permission based on a call from this number not being answered.

Used in several instances of 911 calling back in the San Diego county area.
Or it could be someone with an incorrect telephone mask set up.

JUST RINGS BUSY WHEN I CALL IT.  THEY LEFT NO MESSAGE.