T-Mobile does spam filtering; not sure about other carriers. The default configuration (or at least I think it is, because I don't remember changing it) is to tag the calls by setting the Caller-ID to the name "Scam Likely". You can then configure your phone to respond differently to calls from that ID (e.g. disable ringer). Alternately, if you trust their filtering enough, you can have those calls blocked so they don't ring through to the phone at all. I think it's been working fairly well for me, but I also rarely get legitimate calls from anyone other than a handful of friends/family who are in my contacts list, so I can't be too sure of the false-positive rate.
Unfortunately when I use our conference system’s “call my phone” feature it almost always shows the number as “scam likely”. So I guess the scammers are using the same block of numbers as the conference system.
Info: https://support.t-mobile.com/docs/DOC-38784