Invariably, there's a question before the question. "Should I monitor my daughter's electronic communication?" is usually preceded by, "Do I have reason to be concerned?"
If you have no reason to question your adolescent daughter's whereabouts, friends, safety, or choices, then you're not going to monitor her electronic communication. Why would you? You don't need to know that she prefers puppies to unicorns. And what difference could it possibly make that she has a crush on the lead singer in a boy band? Typical, normal teenage behavior is not dangerous and should be viewed from a discreet distance. Frankly, you don't want too much information. She doesn't like her history teacher? Good for her. I probably wouldn't like him either. Her opinions are her own business. At the risk of giving offense, let's remember why bathrooms have doors. No one wants to know what goes on in there.
When you do want to monitor electronic communication, chances are something has already gone desperately off the rails. "I installed software to oversee her gmail account, but she picked up a hotmail address." "She used her friend's smart phone to contact her supplier." "They use undecipherable codes and euphemisms to schedule unsafe, sexual encounters."
So many rabbit holes, so little time.
If adolescents are using their smart phones to schedule drug buys and unprotected, underage sex, then the smart phones aren't the problem. The drug buys and the unprotected, underage sex is.
So, as always, the fundamental issue is your relationship with your child. Why don't children have respect and affection for their parents? How is it possible to raise "tigers" rather than daughters? (King Lear, IV, ii) Of many reasonable answers, my thought considers parental over involvement as an overlooked dynamic. If the C- in trigonometry goes unremarked upon, the adolescent may feel comfortable disclosing critical issues--those involving reproductive biology and Schedule One drugs, for example. If lesser matters are acknowledged as belonging to the child, she may accept that she is loved for who she is rather than what grades she gets and come forward with important issues.
When parents ask me if they should monitor their children's electronic communication, I enquire about the relationship between the generations. I think about the person asking the price of pork chops to which the butcher responds, "If you have to ask, you can't afford them."
If you need to know what your kids are communicating about with their electronics, we need to back up a few steps: why do the children think you would disapprove? Do they feel accepted for who they are? I would argue that trust begets trust. And that over involvement may lead to deception.
Maybe the answer is similar to "trust but verify." Go ahead and monitor, but only step in if the circumstances are truly life threatening. Ignore, "let's stay up after bed time and text." Pretend you didn't see it because a tired child is not the end of the world. But if your monitoring brings you, "Let's do drugs and have underage, unprotected sex," then a loving parent has to intervene.