Due to having to dial a 9 for external calls, Jabber is unable to make external calls. Does anyone know how to force the Jabber client to use a 9?
Not following here, you can dial 9 plus any number in J4W, on that regards, it's no different from any hard phone, CSS and partitions define what you can dial and reach.
Configure application dial rules to add the 9 or whatever digit manipulation you may need.
If you're on CUCM 8.5 or lower (your post doesn't specify), Don't forget to run the Application Dial Rule COP file afterward to get the database records you created via /ccmadmin into an XML file on TFTP that Jabber can read.