I got a call from "1000". I ignored it and googled it and came up with "SIP Scanning". My Google-fu isn't working to figure out what this is. So what is "SIP Scanning"???
Cutting out a lot of unneeded info, SIP is the protocol that is in charge of VoIP communications setups. SIP scanners are used by less than good intentioned people to look for vulnerable VoIP systems/devices that they can exploit and use for various not so legal things.
It's like a VOIP War Dialer. It's a machine that calls machines looking for other machines, as opposed to humans--with the hope of finding a place to launch an exploit.
Read this book: Ghost in the Wires: My Adventures as the World's Most Wanted Hacker -- It's one hell of an interesting read, and it'll give you an new appreciation regarding how naked "security" measures are so long as there's a human element or known machine protocol in place. Ports are scanned constantly, and various incarnations of the internet are run amok with machines scanning machines, and so forth. Another interesting note, while not directly related--never call back a momentary missed call that you don't recognize. There's a scam where they route your return call to Belize or the Cayman Islands and international charges kick in, sometimes to the tune of hundreds or thousands of dollars per call, e.g. the "One Ring" Scam.