How I can use p4.change in exec task

[jhoomsharabi]

Hi All,
I am stuck to one of the simple issue, I want to use P4Change of Perforce task 
in  one of my exec task the way I am able to use it in P4Edit

<p4edit
    view="//depot/projects/projectfoo/main/src/Blah.java..."
    change="${p4.change}"/>

Same way I want to use it in one of my create-review target under exec task 
like this:

<target name="create-review">
     <exec executable="ccollab">
            <arg value="addchangelist"/>
   <arg value="new"/>
   <arg value="${p4.change}"/>
       </exec>
 </target>

but when I use the way as shown above value of "p4.change" is not getting 
assigned it remains as "p4.change"

[exec] Loading information for changelist `${p4.change}`

the value of p4.change should became numeric "12345"

[exec] Loading information for changelist `12345`

Can anyone help me in this regard.

Thanks