Construction of the internal(extention) 1000

1000 to see how I internal it with my definition of Asterisk?

exten =>1000,1,…

The remaining details depend on information you haven’t supplied.

Please note that SIP phones are devices not extensions, and that is an important decision.

I think you need to and read the book at asteriskdocs.org/ and study the sample configurations supplied with the sources, as your current question is too open.