I don't consider myself to be all that active on social networks, though I'm registered for lots of them -- you can see the full list on my About page. I use Foursquare and Instagram fairly frequently, I use LinkedIn for work often, I occasionally Tweet and almost never post to Facebook. That said, there are two social networks where I'm really, really active -- much more than all of the above networks combined. Those social networks are two iMessage threads on my iPhone -- one between a large group of high school friends spread out around the country and another with a group of friends in NYC (mostly former co-workers). On average, I message my high school friends several times a day and my NYC friends about every other day. It's a great way to keep in touch.

That said, it goes without saying that the iMessage app provides me with an extremely sub-optimal social networking experience. It's annoying that the place where I do the majority of my online sharing has absolutely none of the features of a good social network. Many, many people have these ongoing iMessage threads with their friends so I know there's a product opportunity here.

With that in mind, I'm recommending a product that I think would be extremely useful to millions of people. Here's the feature list -- iMessage, with:

Searchable archives (with advanced search capability by sender, keyword, date and date range)
Photo logging -- all of the photos in the thread should be compiled, easily accessed and searchable
Check-in -- instead of having to tell people on the thread where I am, I should be able to check-in to the location and it should message everyone (I think Foursquare has an API for this now)
Cross platform -- it should work with Android, BlackBerry, iOS, etc.
Group calling feature -- it should be easy to click on a few names in the thread to start a conference call
Payment feature -- if I owe money to a friend on the thread or we're planning a trip somewhere that I need to front the money for I should be able to easily transfer the dollars (the app could sync with PayPal, Google Wallet, Bitcoin, etc.)
Self-destruct option -- for privacy purposes, there should be an option to have a specific photo or text disappear from everyone's phone after it's been viewed for a short period of time (similar to what Snapchat does now)
Share buttons -- it should have the option to share specific text or media on other social networks
No download requirement -- if one of the people on the thread doesn't want to download the app, it should work with iMessage (they'll see the texts and media without the added features)
Reporting -- this isn't critical, but it would be neat to see how many texts have been sent, by who, over a given time period

I realize that WhatsApp has much of this functionality now but it's still missing a lot of useful features.

I think traditionally there's been some hesitancy around building apps for small, closed-loop social networks such as a text message thread because it's only offered to a limited number of users and it doesn't scale well. That may be true, but what's lost in scale is made up for in engagement. I wrote a post a while back about the success of Snapchat and the demand for discreet social networking. Since I wrote that post, Snapchat has exploded -- their users now share 400 million photos per day (more than Facebook and Instagram combined).

I'd argue that if and when Apple, WhatsApp or another app builder releases an enhanced version of text messaging like the one I've described above, they'll see comparable success.