As a teacher and a writer, I have always advised others to make use of their other hand - the hand they don't use for writing. Whether right- or left-handed, we are used to doing so many things with our dominant hand.
Imagine this: you lift the phone receiver/cellphone using your dominant hand to answer a call, then the caller tells you to jot down something, what do you do? Either you put down the phone and look for paper and pen or you transfer the phone to your other hand, then use your dominant hand to look for paper and pen.
How about this: During an exam you are writing down your answers then you come to a problem solving question which requires a calculator. So you put down your pen, take out the calculator and compute. Then you pick up your pen and copy the answer.
What's wrong with these pictures?
You're taxing your dominant hand and wasting time!
If you answer the call with your non-dominant hand, you can use the dominant hand to look for paper and pen and jot down the message.
If you use your non-dominant hand to compute with the calculator, you can take down notes and answer with your dominant hand.
I've seen young people texting with both hands on their cellphones. It's a safety practice specially if they text in public - makes it harder for snatchers to take off with a cellphone held by two hands. But I wonder what they will do if they receive a text message that needs to written down.
I've heard stories of left-handed people who commit the mistake of offering platters of food to their Arab friends using their dominant hand. In Saudi Arabia and Muslim countries, the left hand is used for cleansing themselves while the right one is used for good and polite acts.
Training programs for police, military and security guards emphasize the need to leave the hand used for holding a gun free. If they use that hand to hold a cigarette and an armed enemy approaches, the seconds wasted on dropping the cigarette can spell injury or death to them.
It's never to late to teach ourselves to be ambidextrous.