The following fix is in org master, but not in 7.8.  I am able to use
org-mobile-push.


commit 71089b7e3b00736f854d6e95a52229853262e12a
Author: Bastien Guerry <bzg@altern.org>
Date:   Wed Jan 4 16:37:59 2012 +0100

    org-mobile.el (org-mobile-push): Use `org-agenda-tag-filter'.
    
    * org-mobile.el (org-mobile-push): Use `org-agenda-tag-filter'
    instead of the obsolete `org-agenda-filter'.
    
    Thanks to Charles Sebold for reporting this.

diff --git a/lisp/org-mobile.el b/lisp/org-mobile.el
index b049f4e..bcc1c90 100644
--- a/lisp/org-mobile.el
+++ b/lisp/org-mobile.el
@@ -303,7 +303,7 @@ create all custom agenda views, for upload to the mobile phone."
   (interactive)
   (let ((a-buffer (get-buffer org-agenda-buffer-name)))
     (let ((org-agenda-buffer-name "*SUMO*")
-	  (org-agenda-filter org-agenda-filter)
+	  (org-agenda-tag-filter org-agenda-tag-filter)
 	  (org-agenda-redo-command org-agenda-redo-command))
       (save-excursion
 	(save-window-excursion