A year or so back there was an HN discussion about a service that offered an all-in-one messaging app for most of the major services (including iMessage), but for the life of me I'm having trouble remembering their name. As I recall, they were using a pile of older iPhones that could still be jailbroken and a custom shim to get messages from the phone to their server. Clever, though that method would eventually hit a wall if jailbreaking stopped being feasible.