rolover on "how to rewrite urls"

i don't manage to make a rewrite work. I'm using a plugin to register it:

llamadas/([a-z_]+).html$ index.php?page_id=1051&pais=$matches[1]

If I type in the code manually it works, for example: /index.php?page_id=1051&pais=argentina

Wordpress changes the URL to /llamadas/?pais=argentina and loads the page correctly.

I want the URL to look like "llamadas/countrynamehere.html" and display correctly. I've got the rewrite on top before the others, but no luck.

Any ideas?

Thanks!