Well, the beauty of Asterisk is that you can make it do whatever you want. Quite literally.
If you so desired, you could actually configure Asterisk to alter the outpulsed caller id based on some code you entered before the dialed number.
Other than earning geek points, there is little reason for doing it that way because for all practical reasons, it’s just so much quicker and simpler to use a phone that supports more than one extension.
Pretty much all hardware IP phones support more than one extension. The Linksys SPA-941/942 are an excellent choice.
CounterPath does have a paid product that supports multiple lines. It also has many other features like video calling, presence/IM etc.
The CounterPath product is the best softphone I’ve used. Softphones offered by most IP Telephony providers out there are just custom-skinned versions of the CounterPath product.
If cost is a factor, there are some free/open source alternatives as well…but, again, the CounterPath product, IMHO, is vastly superior to all of them.
Plus, they deserve our support for giving X-Lite to the world for free.
There are also IAX softphones…most of them free. I prefer Dante’s dIAX. It’s not pretty, visually, but excellent in all other respects.