I just find out that you can text from your computer using email.

Just put the mobile phone # into email address in this fashion:

For phone # on at&t network: phone#@text.att.net
For phone # on Verizon netwok: phone#@vtext.com

For mms:

At&T network: phone#@mms.att.net
Verizon network: phone#@vzwpix.com or phone#@mypixmessages.com

You can find out which network a phone number uses from here:

WhitePages – Find People, Businesses & More

Once you receive a text from computer, you can use reply to send a text from your phone to email address that was recieved.