SOAP or REST

If I would like to search calendars/check availability and add events from plone. Which is an appropriate between SOAP and REST
Thanks.

Either should work, though you'll probably find the SOAP interface more suitable for your needs (especially for appointment creation).

Could you please give me an example of creation of an appointment to bongkot@hvlmail.com at 9 Aug 2007 at 10.00 AM
I used this SOAP but it return Internal Server Error.
<CreateAppointmentRequest xmlns=\"urn:zimbraAdmin\">
<m>
<su>SOAP test appointment</su>
<inv loc="2000 Main St., Emeryville, CA 94608" name="SOAP test appointment" type="event">
<comp fba="B">
<s d="20070809T220000"/>
<dur h="2"/>
<or a="bongkot@hvlmail.com" d="bongkot"/>
<at a="steve@hvlmail.com"d="steve" role="ROLE" ptst="PARTSTAT" />
</comp>
</inv>
</m>
</CreateAppointmentRequest>

I have already put authToken in SOAP header

Thanks for help

Is it nessary to put sessionId in Soap header like this.

<soap:Header>
<context xmlns="urn:zimbra">
<authToken>token is here</authToken>
<sessionId id="9"/>
</context>
</soap:Header>

<sessionId/> is not necessary, but if you don't specify either a <sessionId/> or (better yet) <nosession/> then you're going to start accumulating 1 session in the server per request, which is bad.

If you want to see sample valid SOAP for your server version, turn on the debug window for the AJAX client and use the app. All the SOAP sent between client and server should appear in that window. (Search the forums for instructions on how to turn on the debug window.)