Hi GOLdFi-sH,
You can definitely remove add-ons during an agreement. If you are referring to a data add-on (with a data agreement) then you would incur a device savings recovery fee (early cancellation fee). The way it is calculated depends on where you reside as well as when you began the agreement. You can contact customer service to find out the exact amount.
All other add-ons such as voicemail, call display with name display, long distance, etc. would be able to be removed at any point within incurring any fees.
