Those launch/launchctl commands didn't work for me either. What did work was to install the command-line utilty open from Cydia and just execute
open com.apple.calculator
Notice the lowercase c in calculator, that was the bundle identifier for my calculator app.
Here's the developer's website for Cydia stuff:
http://kramerapps.com/cydia/
This links to the repo site:
http://moreinfo.thebigboss.org/moreinfo/depiction.php?file=openData
Update: For iOS 6.x, this current version of open doesn't seem to work. See @Nate's answer to another question linked below in the comments.
Update 2: The open package in Cydia has been updated and now works with iOS 6.
Update 3: Here is the source for the package: https://github.com/conradev/Open.
If you look at the open.m file, you can see that the function SBSLaunchApplicationWithIdentifier from the SpringBoardServices private framework is what actually opens the app.