You can use email to send a text message to a cell phone, but you have to know the service provider (AT&T, Verizon, etc.) of the recipient's phone to do that.

For example, if you're using email to send a text message to someone with an AT&T phone, you'd send the email to 5551234567@txt.att.net, where 5551234567 is the recipient's phone number, of course. For someone on Verizon, you'd use 5551234567@vtext.com.