I've been using Rhino on GAE for over a year now and I'm happy with it. I haven't run into any compatibility issues. If you want it to, it even compiles your javascripts to java bytecode on the fly which makes it even faster. Also Rhino won't do extensive classpath scanning that would add to your instance startup time.
I'm just wondering why wanted to go that road in the first place. Isn't your phonegap app meant to be run on the phone? The kind of backend service and its implementation language shouldn't matter at all. Maybe I did get you wrong. Greetings - Wolfram -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to google-appengine+unsubscr...@googlegroups.com. To post to this group, send email to google-appengine@googlegroups.com. Visit this group at http://groups.google.com/group/google-appengine?hl=en. For more options, visit https://groups.google.com/groups/opt_out.