If Symbian really was that popular, then you'd see more apps and games on it, and not Windows Phone and Android.
Again, I said it WAS popular. This is not disputed, it had 42% of the market in 2009. I am sure app support has something to do with it, and why Windows Phone will never threaten iOS and Android unless it gets improved app support.
Windows Phone is becoming increasingly popular, and is getting more support leading up to the big release of Windows 8. I just read an article about Symbian (now called "Belle"), and basically everyone has abandoned it in favor of Android and Windows Phone. I don't care about the marketshare from 3 years ago, that's irrelevant, and has nothing to do with how popular it is today. As far as support goes, Windows Phone has more developer support than Blackberry and Symbian/Belle. Most of the apps made for iOS and Android are also being made for Windows Phone.
You can hate on Microsoft and dismiss their achievements all you want, but they are preparing for an onslaught of marketing this fall, and they are going to heavily push Windows 8, Windows Phone, and the whole Metro interface. Microsoft is aiming for complete convergence, where apps and software are shared between devices and the "cloud" (SkyDrive).
Microsoft has the money, resources, and manpower to make Windows Phone a success. They did it with Windows PC, Office, and Xbox.
Google's advantage is that everyone uses their search engine, and they make a shitton of money from internet ads and revenue. The main problem with Android is that it's so fragmented, there is a large gap between users who have the latest version, and those that are using older versions. Google has been doing a terrible job sending updates to users, relying on carriers to do the job for them. Apple releases their updates in a timely manner, and it's easy to update just by syncing to a PC and logging into iTunes.
And pretty much everyone is calling Blackberry/RIM a sinking ship. The company is losing a ton of money, and their management is in shambles. Blackberry is primarily a business phone, but a majority of people have switched to the iPhone or an Android device. RIM lost the opportunity to fight Apple and Google with a mass-market device, and they are now facing the consequences.