It's not very exciting, but InstaMessage perfectly adds a much-needed chat feature to Instagram. It looks like the people behind Instagram designed it, and it actually has an active membership base. It even lets you control parts of your Instagram profile, but its marquee feature is the real draw.
To make this app work, you have to log in with your Instagram account. Once you do, it feeds in all of your Instagram friends, but you can only message them if they use the app, too. You'll probably have to invite most of your friends before you get started. While you're waiting, you can search for nearby users or browse the most popular users on InstaMessage. Messages move quickly, but you'll have to guess whether or not your friends are actually online, because the app never really makes it clear. You can't send smileys or set away messages, either.
This app solves a problem and does it with style. However, InstaMessage could use some more features to round things out. Still, if you want to make new friends on Instagram, then this is a neat way to do it.