You should be able to use the SMS Gateway for the other people's phone carrier to send them SMS.
Here's a fairly comprehensive list of gateways. But basically you would address the email as
. Email to SMS Gateways, Complete List | mutube
It will be an email on your side, but an SMS on their side. Sadly, it doesn't work in reverse though. They won't be able to send you messages without sending them to your actual email address in you are trying to avoid SMS charges.