Create a template tiddler called ContactTabTemplate with the following content:

<$set name=currentTiddler value=<<currentTab>>>

    {{!!text}}
    
</$set>

You can use any method you like to set the current tiddler. Note the blank lines to force the text field to be transcluded in block mode.

Then add a template:ContactTabTemplate parameter to the tabs macro used to render your contact tabs.

The TiddlyWiki documentation gives the following equivalent version using the $transclude widget, which we've so far mentioned only in passing, and the $tiddler widget, which we haven't seen at all:

<$tiddler tiddler=<<currentTab>>>
<$transclude mode="block" />
</$tiddler>

We'll talk about both widgets in chapter 7.

Another way would be to transclude the tiddler named in the currentTab variable using double curly braces, since doing a transclusion this way sets the current tiddler as it does so. You have to use text substitution to get the value of currentTab into the braces, though:

\define makeCurrentTiddler()
    {{$(currentTab)$}}
\end

<<makeCurrentTiddler>>

But when you reread this one later, it'll be much less obvious what you were trying to accomplish, so one of the preceding methods is probably preferable.