This is mentioned several times on here in other threads. You can change them by disabling the stock apps and/or choosing your third party apps as the default.
For texting, you need to go into the Settings Menu>Apps>All>Texting and disable it. Ignore the popup. If you have a 3rd party text app (e.g. Handcent, Chomp, etc) it it replaces the stock one on your lock screen. You should also make sure it's the deafult prior to the above steps in the app's menu.
For the dialer, open your Contacts, and if you haven't already done so, hit the phone icon on the bottom, which should give you a popup asking which dialer app you want to use as the default. Pick your app (I use Dialer One) and it will replace the stock app on the lockscreen.
For the camera, I forget the steps exactly as I haven't replaced that one, but I did see steps for that somewhere. It had to do with picking your own camera app as the default, but you'll have to dig around for that one.