Apple's iMessage platform is great for heavy texters. Integrated deeply into the bowels of the operating system, iMessage simply disappears so normals are completely oblivious to the fact they're actually using the system. When you start typing a recipient's name in the stock Messages app in iOS or OS X, iMessage checks with Apple to see if a person has iMessage enabled.
If so, the chat bubble turns blue to indicate that the message will be sent as an iMessage, thereby bypassing your carrier's SMS service. Problems arise when you switch to another smartphone platform only to discover that your phone number has not been removed from your Apple ID.
As a result, this could turn your phone number into a black hole for text messages...