Those launch / launchctl didn't work for me either. What was done to install the open command line utility from Cydia and just execute
open com.apple.calculator
Notice the lowercase c in calculator, which was the bundle identifier for my calculator application.
Here is the developer's site for Cydia:
http://kramerapps.com/cydia/
This is the link to the repo site:
http://moreinfo.thebigboss.org/moreinfo/depiction.php?file=openData
Update: for iOS 6.x, this current version of open does not seem to work. See @Nate's answer to another question mentioned in the comments below.
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 will see that the SBSLaunchApplicationWithIdentifier function from the private structure SpringBoardServices is what the application actually opens.
source share