Paul Rob> 303 and 720 are overlay area codes for the same place, the Denver
NEVER SAY NEVER!
Right now, there happens to be no assigned 303-720 nor 720-303 office codes. But read on further down -- I will repost what I originally said back in mid-July when this thread originally appeared. Neustar-NANPA, the assignment body for US-based NPA-NXX office codes does NOT flag either 303-720 nor 720-303 as "NOT to be assigned" in their web-based databased. Afterall, this is an overlay situation, and since ALL TEN DIGITS MUST be dialed, in the long run, there is no conflict or ambiguity with such assignments. And inn some overlay areas, the same digit combination is used for NPA and an NXX within that NPA!
You also might want to go through some of the entries in NANPA's NPA-NXX assignment database. In some cases, there are indeed flaggings of 'UA' which means unassignable -- i.e., NOT to be assigned. And this is still the case with certain combinations in overlay areas. But that doesn't mean that in the next ten years or so, when ten-digit dialing and overlays becomes more the norm throughout the US and Canada that such combinations won't still be flagged as not assignable. And as I mentioned, there are such assignment situations in some places already.
Even in places where there aren't yet overlays or mandatory ten-digit dialing, there are some cases where the numerics of an adjacent NPA code, even one which is adjacent with local calling arrangments -- those numerics can also be used as an NXX office code in other adjacent local NPA codes. The ambiguity is usually eliminated by the use of a mandatory 1+ before ALL ten-digit calls, regardless of whether the ten-digit number is local or toll. And all "home" NPA calls in such area codes is still permissive as "just" seven-digits, sometimes without differentiation as to local vs. toll for that seven-digit "home" NPA call.
And here is the orig> I got a call yesterday on my Sprint cell phone from 303-720-1234.
It is bogus. 303 is the area code for the Denver CO Metro area. (At one time, the entire state of Colorado used 303, but that was some time ago). 720 is being used as a central office code within the 303 area code in your situation, but the 720 numerics as an area code also happens to be the overlay area code for the Denver CO Metro area. Since ten-digit local dialing is mandatory within the Denver Co Metro area of area codes 30 303 and 720 in overlay, there isn't anything "wr-ng" with having a 303-720 code, nor a 720-303 code, nor even a
303-303 or 720-720 code. Ten-digit local dialing is mandatory in overlay areas.However, it happens that at this time, there is no such 303-720 code assigned in the Denver CO Metro area. I looked up the central office code reports at NANPA's website,
So, you probably got a call from a telemarketer sending bogus caller-ID information. Typical. :(