I too just got a call on my cell from 781-981-5500. I didn't answer, which is what I usually do if I don't recognize the caller or number. Caller didn't leave a voice-mail, which is a further sign that it's not someone with a real reason to reach me. Number is registered to MIT Lincoln Labs in Lexington, MA. Someone is spoofing.
I see I reported this call last February and this time the ID comes up as MIT Lincoln Labs and of course there's no message. My phone number is just a voice mail service so I have no idea what the call is about nor do I care. I have found that shorten the "ring" to my number has dimished a lot of the unsolicated calls. Let them deal with an answering service as they are just wasting their time calling my number as they will never get anyone to answer a phone that doesn't exit.
Any call from MIT Lincoln Labs will show up as 781-981-5500. Could be someone you know who can't use their cellphone trying to get ahold of you. Odds are it isn't a solicitation call.