[Q] Which model is my Nexus S exactly?

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http://forum.xda-developers.com – Total noob here.I have a Galaxy Nexus S GSM phone running ICS.I do not know the exact model I have I suspect I am having the M200 variant.The guy who sold it to me in all probability rooted it to install ICS.I want to install Jelly Bean on it.My questions are(Please forgive the wall of text, I wanted to be as elaborate as possible) 1) How can I know if my phone has been rooted ? Can you install ICS without rooting and without an OTA update?I dont know what the previous owner did. I found out that I have an unlocked bootloader.But When I try to install and run Voodoo Sound which requires (HowTos)