Depends on what you want to do. I admit I didn't know what iMessage was capable of, but the basic features (text, images) are also possible with XMPP. The more complicated ones is a mixture of "the ISPs don't allow that" (I'm thinking accepting inbound connections), "the user needs 3rd party support" (I'm thinking about needing a proxy server for transfers, which most people don't have, but Apple can conveniently proxy transfer through its own servers) and "just do it".
The problem with XMPP (or any IM protocol for that matter) is that if nobody uses it, there will be little technical progress, which means few people will use it, etc...
Email? Really, now that everyone has email on their phones, why bother with SMS or these SMS-like systems? Email is more reliable, more flexible, and seems to be just as fast in practice.
The smallest email in my inbox right now has 913 bytes of headers and 132 bytes of content. Between the various hops, including through a spam filter, it took 13 seconds just to land on my server. It was then an additional 0 to 300 seconds before each of my devices knew it existed, because push remains black magic when dealing with clients and servers from different authors/companies.
This is not comparable to the normal performance of SMS or iMessages.
Except there is no email app that I know of that presents conversations in way that is as easily readable as line, messenger, etc. I wouldn't want that either as the current presentation is perfect for large amounts of information that I get in my other emails.
The reason iMessage works well is because it's integrated tightly into the OS. So for an open-source alternative to be competitive, it would have to run on... an open mobile OS, which would in turn require open hardware.
Heh? Have you tried solutions like Whatsapp, GroupMe, or Viber? They all work absolutely fine on both big mobile OSes, regardless of hardware.
I don't see the need for absolutely open hardware for an alternative messaging system. Sure, they aren't FLOSS solutions, but they are much less closed than iMessage and are cross-platform.
Fine, but Viber does, right? There are open source, secure messaging systems on the way too. My point was that you do not need open hardware to have a relatively open messaging system. Just look at IRC as an example. It might be somewhat dead now, but it certainly runs on everything now.
Sure, you can use proprietary hardware (iPhone) and try to make it run different software, but your luck getting around their protection systems may vary (and it may or may not be illegal, depending on how much you care).
Curious: has this even been tried? I would assume Apple SoC's require binary drivers, so even though they are similar to Android phones on a hardware level it might be difficult or impossible to even get an Android port to boot.
Hell, it can be difficult to get an unsupported version of Android to work without major bugs on an Android phone.
Important to point out: the authors of iDroid stopped, but not due to any technical obstacle; it was mainly because iDroid was a hobbyist project and their lives intervened. Someone else could pick up the effort today, if they wanted.
However even if someone picked the project up again it wouldn't run on any modern devices, since the last iPhone to have an untethered bootrom exploit was the 3GS.
