This is a off-shore "generic" drug seller.  They spoof local phone numbers but are routed thru Cayman Isl. from India.  Don't bother being polite - just hang up.

someone keeps calling from this number to my cell phone and when I answer they say nothing at all so I just hang up. tried to call them back and get a busy signal. the only caller id is the phone number. 4 calls total with in two days so far. not answering the next time

I also get calls from this number.
They are advertising mortgages.  I think they got my number from the internet when I was shopping for a mortgage so:
DON'T FILL OUT THOSE WEB BANNERS!!!!!
Not like I need to tell you this :( But I guess I was just kinda curious.

I plan to report the number to the FCC, at lease that is what I was told to do by the local authorities.
I recommend you do the same.

Also after searching the internet for a while I found that it is a sprint number so I plan on lodging a complaint with them as well.

I believe it is a prepaid wireless number.

this is the online complaint form from the FCC:

http://esupport.fcc.gov/complaints.htm

Yes I Have also and just now i told the guy to take my name off of his list and he told me TO F--K OFF IM GOING TO TRY TO FIND MORE INFO ABOUTH THIS NUMBER