As I outlined in a previous post, I don't know the email address people use on their phones or if they have them set up. If people get an email message they can't just "call back" either. Its unpopular, I've never once used mobile email.
In your Contacts list, you can add email addresses, so you'll never have to memorize them. When they get an email from you, they can select your name and choose to call you back. This functionality is available in all smartphones.
If mobile email is so unpopular, then why does RIM have the highest share of the Smartphone market?
I'm currently a BlackBerry user, and I curse when people send me text messages. It costs $0.15, rather I want to receive it or not.
Fact is, SMS is far more popular than email and voice calls.
I think you might need some statistics before you call that a fact. Voice calls are still the most popular form of mobile communication. I'm judging this, of course, by the number of bad drivers (phone to ear, one hand on wheel) and bionic listeners (Bluetooth headset users) that I see every day that are actually using their phones to talk to people.