Looked and that code is 55

Just tried it.
set it to index 900

So we have to put in 55900 to have it dial out.

Here's another problem we have now.

A call comes in, if we are busy we need to transfer to this Abbr dialed number.
But it doesn't allow us to release the console.

Only the console and the new number will be connected not the caller who called in.