It would certainly be possible to do this with Asterisk (or one of it's distributions - Elastix, trixbox, pbx-iaf..) although that may be overkill for what you're trying to do.
To do it with Asterisk you'd need -
- A server running Asterisk! (could either be local to you or a VPS/dedicated somewhere)
- A voip service provider (to terminate your outgoing call on a normal phone line)
- VOIP phones for your sales people (either using a normal phone and the adapters you brought/softphone running on a PC/voip phone)
- A click-to-call script (I've hacked this
around before and implemented it for someone)
Like I said, it would work but hopefully someone knows of a simpler solution? :-)