Learning lines

Well, I have been cast as an understudy and need to learn lines for 2 characters.  Ahhhhh, how does that happen? What do I do?  
First, I bought an iPhone app. So far, it's fabulous and a big help.  I bought Line Learner.  So far I'm loving it and it's a great help.  I'll let you know in 2 weeks when I have to be off book!
Here are some other links I've found to help learn your lines:
Learning Lines for Actors
How to memorize lines

It also helps if you go to rehearsals (even if you don't have to) so you can listen to the actors say the lines.  Instead of just listening to your voice over and over on your ipod or through the app you've just bought.

Let me know if you have any other suggestions.