Is call manager needed for VoIP?

[admin_2]

when would a call manager be needed when setting up VoIP?

in other words, if I need the following..

pstn<->5300<->7200<==>7200<->5300<->pstn

would I need a call manager and gatekeeper?

[#2]

No need for call-manager, callmanager is like a ip based pbx/switch, providing class5 like services. Gatekeeper is optional, normally gatekeeper is recommended for complicated voip network impelmentations.