Called. Left no message. Tried to call back and either busy or no answer...

The caller left no message.

Same story, no message.  I called back and get a busy signal.

Got a call from the number. They left no message and no one answered when I called back.

I was on a call when this number came in.  looked online first to see if it was residential or company.  called back, busy signal.

After a little searching, it appears to be either from a telecommunications place in Mesa/Phoenix, AZ called Eschelon Telecom, Inc, which is now acquired by Integra, or a customer on their service..  I work for a different telecommunications company here which from what I know you should be able to  call Eschelon/Integra and tell them to block this number due to annoyance calls.

Eschelon Telecom, Inc/Integra is a call center. This is a telemarketing outfit... they run any number of campaigns, so you don't really know who they are marketing for, but they are a callcenter non-he-less.