Is online communication a solved problem? Do you see any scope of improvement?
I'd use it as a back-end;a way to archive everything I say online in any format. Include pictures/files sent, maybe include those linked as well. And include correctable transcripts of audio in metadata for searching.
See the competition now between Gmail, Hotmail, Yahoo, etc. Consider how they could vary their services if they were all cataloging that much more.
Maybe I'm idealistic, but I think there's still room for a "Google moment" where someone comes along and does something else so well, we're amazed that everyone hasn't always been doing it that way. Though honestly, at this taste, Google may just get there first.
Now, your phone, email, IM, SMS Facebook/Twitter/Google are all separate 'things'. I think we're in the early days of convergence, where all of these things are smooshing together. Think Google Voice (phone/sms) in your mailbox, or IM along with Voice/Video (Skype). And we still have too many identifiers... your skype id, your twitter id, your google + name, your home phone number your office phone number etc. etc.
I really think the 'next big thing' will be the collapsing of all of these ID's and services into one agregator(probably google). I'm not saying it's a good thing, or that it will go smoothly, but it will happen.
If you're interested in building a business, then there's a huge amount of opportunity the online communications space!
I could probably think of 5 cushy niches that will print $20k-60k per month with a very small team. Just look around you and identify occupations that involve communication and build a communication product around that occupation's process.
It's a relatively simple and straight-forward process to building a business that lots of technical folks overlook because it's not sexy. I'll take profitable over sexy any day.
Tone of voice problems might have a technological component to the solution (c.f. spam).
Automatic translation needs improving. Yes, it's incredible what's been achieved, but the translations are low quality.