Some Airlines have a facilities where you can make use of your mobile phone just like in the ground. So you don’t need to switch off while in the flight except maybe during take-off and landing. The technology call OnAir. Not all Airlines company have it. So if you are just falling in love with some one and must text your partner every 5 minutes then seek Airlines with OnAir Service.
Read more about OnAir here. I read that Air Asia have it. Others like Qatar Airways, Royal Jordanian, Saudi Arabian Airlines..