Changing the lock screen

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http://androidforums.com – Ok guys I have a question I am thinking about changing my txt messaging app but want to know if I can change it to where it is on my lock screen like the stock messaging app is. I am using a droid razr at the moment. If I can't change what app is on my lock screen i guess it is kind of pointless to change my testing app. Thanks in advance guys. (General)