Does Android poll for APN availability? I am waiting for my carrier to set up private APN for my company. I have already configured my Android device with settings provided by them. Currently packet transmission is not working. Will it work when carrier finishes his job? Is device restart needed? Or disabling and enabling packet transmission?
A reboot might do it, or reselecting your network provider, but I've often found that a factory reset is needed for Android to properly pick up APN settings automatically.

However, since you have manually entered the information it should work pretty easily.  I would reboot, but turning Airplane Mode on and off should be sufficient.