iMessage is Apple's awesome free messaging service that works beautifully for sending text, picture, and video messages (even group chats!) - not just between phones, but also to Macs and iPads too. Our favorite feature is being able to continue a chat thread on our laptop that we start on our phone - something that regular SMS does not allow.
When it first came out, many people were still paying for each SMS text messages, so iMessage was initially an awesome money saver too.
But a major bug has been making news lately -- if you have been using iMessage on your phone, and you then switch away from iOS to another smartphone platform without turning off iMessages first - other iOS users will no longer be able to send you text messages anymore. These messages have been getting sucked into an iMessage black-hole, and thanks to a server glitch even Apple tech support for a while was unable to fix the issue for users who suddenly found themselves unreachable.
Fortunately - the server glitch has been fixed, and further improvements are coming. So if you are a former iMessage user and have been having trouble with lost incoming messages, check in with Apple now for help getting things back on track.
And if you want to avoid the problem in the first place - deactivate iMessages BEFORE you switch to a new non-iOS phone!