Registering IP phone

I am new to asterisk and I recently set up an asterisk server on Ubuntu
and got a couple of PSTN phones to work. Now I am trying to get an IP
phone to work and I am stumped on getting an IP phone to register.
Do I need a SIP service provider for my SIP phone to register to or
can I get my SIP phone to register with my asterisk server and make
calls to and from extensions?
I am running asterisk 1.8 on ubuntu 11.10 and I have Grandstream 1405
IP phone. Are there any tutorials? Any help is greatly appreciated.
thanks … o+Asterisk

Thank you kindly. That was short and sweet and it worked.