It can be done, but it depends on their service provider as far as how you have to format it. Like for instance, with verizon its phone-number@vtext.com
Not sure of the formatting on other service providers though, sorry.
There are websites that list the emails for all the carriers. I am late for work though, and shouldnt be fluthering anyway. Or, you can have them send a text to your email, then respond.
you can also check out google.com/voice. Google voice is a great service and i use it to send and receive about 200 texts a day through my email. If you need an invite i can provide one.