This issue pops up every once in a while. The reported deadline has been changing for years. Contrary to a popular email chain letter, cell phone numbers are not in any danger of being released to telemarketer, and you do not need to register that number with the Do Not Call list. These panicky emails have apparently sprung from a misunderstanding over the creation of a cell phone directory. Mobile phones have traditionally been excluded from phone books but many people are now using these phones in place of landlines so a push was made to have a directory of cell phone users- a wireless 411 directory. (The project has hit a number of roadblocks but none of them concern the sale of information to telemarketers.)
Adding your mobile phone number to the Do Not Call list will not have any adverse effect but neither is it a necessity.