alt Hacker NewsWell... They are registers, so yes. The question is whether it'd make sense to do it and what problem would that solve.
In a past life, I taught young programmers you can, of course, make a phone number a numeric field in your database (and save a couple bytes by doing that!) but it'd only make sense if you wante to figure out the average phone number for all your clients so you could call them all at once.
There are extreme cases where it would actually make sense, but that I usually left to dig into in a later discussion.
How do you represent a leading 0?
I don't know enough about phone numbers to say whether you could encode them as an int anyway. In the UK all standard numbers start 0 and international codes start 00? Of course you could introduce a 'locale' and then 20 years later try to solve that mess with multiple ways of representing international numbers. Or maybe not teach young programmers that you can make the phone number a numeric field?
So it seems to me the solution is to save them as BCD...