All we have so far is a press release from Universal, which doesn't say how many theaters the sing-along edition will be in. You are encouraged to visit the Mamma Mia! website for updates, however. These will be regular screenings at regular movie theaters for the regular prices; all that's different is that the lyrics will be on the screen, karaoke-style. And the best part is, even if you're a terrible singer, you can take comfort in knowing you're still better than Pierce Brosnan.
ABBA's music is famous for being catchy, and as a result many people overlook the actual words. This sing-along event will be an opportunity to really notice and pay attention to the subtle complexities of lines like this, from "Money, Money, Money":
In my dreams I have a plan
If I got me a wealthy man
I wouldn't have to work at all
I'd fool around and have a ball
Hooray for girl power and rhyming!