thats not completely accurate, when you email to a person's text message email address it will come to them as a normal text message. For example, if you email [email protected] its will send a text message to that number's phone like it came from you texting them.
They can reply to that and it comes to your email. Im not sure how the 15 min delay works. sometimes i have a delay sometimes the email is instant it really seems to depend on the day and account. If its your BB email address it seems to get there pretty quick. Still a good substitute for paying outrageous text charges