Problem with WRT/Flash ExternalInterface

I'm doing a WRT app that uses flash inside. The thing is i have to pass parameters to the swf via javascript. So i created a function in javascript like

[CODE]function returnFunction()
{
return "test";
}[/CODE]

and in my SWF i have the following code:

[CODE]import flash.external.ExternalInterface;

var result:Object = ExternalInterface.call("returnFunction");
versionTxt.text = "Returned: " + String(result);[/CODE]

So, this works fine when i run on my local machine(had to change some security on the flash player) and when i host it on a server. But i have to run it on a mobile phone, so i wrapped it in a WRT app, but when i test it, it returns like:

Returned: null

So i'm out of options here, is it a security problem? I guess i already saw something like this running in WRT so i'm quite sure it's possible, just don't know what i'm missing here :/