If we are defining "mobile" as "phone" then the poll is valid. If it includes tablets and similar devices then my vote is Windows 8.1 ProWMC running on my Microsoft Surface. Otherwise, I vote jailbroken iOS for usability, then Android for being open source, and Windows Phone for trying to be similar to my desktop.
1.Android 2.Symbian [but it's like dead now since nokia moved to windows mobile,but i'm still using it]
My first smartphone was a Galaxy Nexus running Android Jelly Bean 4.1.2. However, my use on that smartphone has diminished recently because I got an iPhone5 as a gift from one of my mom's sister's from a country called Laos (which is between Thailand and Vietnam). I also have an iPod Touch music player as well running iOS6. I didn't tell you this but that iPhone that I got as a gift - also runs on iOS6. For technical reasons, I resisted on upgrading to iOS7.
Simply Android, Google Android OS is the most popular open-source software created by Android, Inc. and was purchased by Google, Inc. If you have an android phone, you are familiar with the Google Play (formerly known as Android Market) where you can download ranges of apps for free or for a fee.