If my phone service is disconnected, can I still use the number to iMessage? Under my setting in iMessages it only allows me to select my linked emails and the telephone number is there but grayed out and i can't seletect it !

If my phone service is disconnected, can I still use the number to iMessage? Under my setting in iMessages it only allows me to select my linked emails and the telephone number is there but grayed out and i can't seletect it ! It wont activate. I just recentely got AT&T. When I had verizon before and my phone got disconnected it allowed me to still iMessage off my number.