I didn't recognize the number, and so I let it go to voicemail about 5 times over the last couple of days, but no messages were left. Finally I answered, and the pre-recorded message says "Steam clean your carpets for only [blah blah blah blah]..." Sons a [***].
I had thought I was registed on the national "do not call" list, but apparently I was not. I just registered. It's free, and should stop calls to your mobile within a month. If you are registered and a telemarketer calls you, you can file a complaint on the site.