[Asterisk-Users] is gatekeeper required?

[ml_asterisk-users at rajnoch.sk]

Hi all,

I have one asterisk server with one ISDN BRI connection to PSTN,
with h.323 support (oh323)

I buy some voip phones, and I connect them to the same switch as asterisk
server is; all is at the same TCP network.

I need to route some extensions from my DDI (DID) line at asterisk to
some voip phones, and also to do:
outgoing calls from any voip phone to PSTN via asterisk, and
intermediate calls among voip phones themselves (each other).

my voip phone has own IP, so I can route incoming call to them by:

exten  => 59305005,1,Dial(H323/${EXTEN}@192.168.0.11)

My question is how can I do outgoing calls?
Need I call firstly IP of asterisk and then to enter phone # to PSTN?
respectively, how can voip phone knows to which IP to connect?
Is this problem solved by gatekeeper? need I one.

Is there anywhere a BIG PICTURE (scheme) how asterisks can work with
voip phones (h.323)?

THANK you very much for help.