Don't suppose you have any non-US numbers in there, the 3-3-4 pattern is not universal. My Company Phone book application has to cope with 2-5-3 and 2-3-5 as well. And then there is adding the international prefix....
And even in the US, not every number follows the 3-3-4 pattern. Local numbers are often given as a 3-4 pattern.
Non local numbers may, or may not, have a '1-' prefix.
Some numbers are given using letters (1-800-RUN-PERL).
And then there are numbers like '911', which don't fit in.