They are assembling active cellphone numbers lists which they then sell to telemarketers. Do not answer the call. If you do, they know your number is active and you go onto their list. That is THE purpose of caller ID...don't answer calls from numbers you do not recognize..
Just got a call from this number and when I answered they hung up. I tried to call it back because it showed up as a Florida number and I have a Florida number so I thought maybe it was someone I knew, however when I called back I received a recorded message stating that my call could not be completed as dialed. I have sprint so I don't think it's just T-Mobile customers.