My new cell phone can't be called from some numbers. Why?

Factual Questions
1

My dad recently got a new cell phone, VoiceStream. When he is at work, my mom can’t call him from within her company(she presses 9 to get an outside line). It simply says, “Please hangup and try again.” VoiceStream says it is Planet Acess’(the phone system my mom’s work uses) fault. They say Planet Acess has to register the number. Planet Acess says that Voice Stream has to activate the number.

Ever heard of anything like this? We have tried switching the number and several other things. Any advice?

2

Is your cell phone number’s prefix new for your area code? I had the same problem at my work when a bunch of new prefixes were issued. They made some sort of change to my work’s phone system and everything was fine.

Haj