I only found during my research solutions that either involve a modification of the APNs, or are not compatible with Android 2.3 because of its enhanced security.
Nevertheless, I am pretty sure there is a faster/cleaner way than modifying the APNs to enable/disable mobile data connectivity. Indeed, one of the most popular widgets on the market manages to do the switch very quickly and claims it does not touch APNs.
-> Do you know which API/function I should use to get similar functionality in my app ?