would lead to the [ \.-] character class for the two separation regions. Although I must say I've never seen anyone use a period as the separator in a phone number, but just because I haven't seen it doesn't mean it doesn't exist, just that it's not common in my little corner of the world.
I don't know what the reasoning for it is, but I have seen it in some places, usually done by North American businesses. I always assumed it was somehow related to fonts on business cards or the like, or maybe just a desire to be different.
