SIP clients for Asterisk

I’m wondering what clients commercially available work with the asterisk pbx. I’m particularly concerned that a client supports all (or most) of the telephony features offered by asterisk. How do we ensure a client suppports such features? Further, where can I find out how asterisk implements various telephony features (e.g., call transfer, conferencing) using standard SIP primitive methods? I.e., where are the call flows documented?

Thanks!

  • GD