I’m wondering how to setup 2 Click2Call buttons which use different SIP accounts and different callee numbers.

For example:
First button connects to SIP server #1 and calls to number1.
Second button connects to SIP server #2 and calls to number2.

Answer:

You can use dynamic scripts instead of the default scripts account.xml and callee.xml.
For example: account.php and callee.php. It should be your own scripts such as PHP, Rubi, JSP, ASP, CGI or other simple script which returns valid XML output similar with account.xml or callee.xml.
Your dynamic scripts should be set up in config flashphoner.properties. You should replace corresponding settings with account.xml and callee.xml.

Click2Call.js is a main script of client side click-to-call implementation.
The function loginByToken(token) is used for SIP authentication and callByToken(token) is used for calls.
For example, you can implement case when the first button will do loginByToken("button1") and callByToken("callee1")
and loginByToken("button2") and callByToken("callee2").

Example:

Authentication of the click-to-call button:
1. loginByToken("button1")
2. WCS sends a request to your PHP script: account.php?token=button1
3. Your script returns XML for first SIP server account (similar as account.xml).

Call from the click-to-call button:
1. callByToken("callee1")
2. WCS sends a request to your PHP script: callee.php?token=callee1
3. Your script returns XML for the first callee number (similar as callee.xml).

The same is for other click-to-call buttons.
You can get additional information here:

http://docs.flashphoner.com/display/WCS/Click2call

http://docs.flashphoner.com/display/WCS/Click2call+Quick+Start