I use iMessage constantly, and while the lock-in bugs me theoretically, everyone I need to talk to regularly uses iOS, so it does not actually practically affect me very often.
The last time I can recall it being an issue was when I went to message someone who was SMS-only from my iPad. The whole SMS-overloading thing for iMessage is the most effective/profitable marketing decision Apple has ever made, I think.
I mean, when Hangouts finished Voice integration it will do all of that and more. It can already cross conference in VoIP and PTSN users, when they finish GV integration, you'll just text/chat with another Hangouts user and it won't matter if they're on their smartphone, dumbphone or laptop.
The last time I can recall it being an issue was when I went to message someone who was SMS-only from my iPad. The whole SMS-overloading thing for iMessage is the most effective/profitable marketing decision Apple has ever made, I think.