IPhone :: Any Limitations For Sending Animated GIFs In IMessages?

What is the deal with animated GIFs via iMessages on the iPhone? Does it work? Is it supposed to? Are there any limitations? I tried sending an animated gif to a friend. Both of us are using an iPhone 4S running iOS 5.1. On my end, I see the animation playing on the iMessages app. On her end she just receives a still frame. Why?

I tried it two different ways. First I tried it by simply copying the image from Safari and pasting it into the message. Then I tried it by saving the image to my camera roll and adding it to the message that way. Neither worked. Both times I could see the animation on my end, but the recipient only saw a still image.