Well. If you are talking about a ITSP (internet telephony service provider) providing you with service. Then the provisioning is done on there end. They will set it up so you asterisk server can “talk” to there systems. Most of the service providers will then provide you with some sample configs.
Most of the time you will receive a sample configuration the will set up a peer in you sip.conf (assuming that is the technology you are using with your provider) That will look like a standard peer in sip.conf and allow you to send call to the service provider to have them sent to the PTSN. If you plan on havening this provider terminate call from the PTSN to you the will most likely provide you with a register string to place in the [general] section of sip.conf. That would look like this
register => username:firstname.lastname@example.org:5060
That string will allow you asterisk server to “register” with your service provider so there know where to send calls that are meant for you.
Now with that said you can “provision” phones or ATA’s yourself. Again assuming you ATA is using SIP you would make a friend (or peer depending on what you are doing) in your sip.conf and then tell the ATA (through the firmware) where it is to register (i.e. the ip address of your server)
Hope that helps.
What book are you reading? I hope it is this on Asterisk: The Future of Telephony I have self tought myself with plenty of tech books and none have helped me more so than this book. I still consider myself a novice when it comes to asterisk but I would have no clue what was going on with out that book.