This support article is for US customers, however, the same could apply to international carriers.
Basically, you take the phone number you want to send the text to, and then add the carriers email protocol to the end of it.
For example, I have an AT&T number so mine would look like 3175555555@txt.att.net
I would then take 3175555555@txt.att.net and place it in the email to box.
That's it. Now all my new form submissions will be sent to my mobile as a text as well.
Here is a list of carriers and the email extensions:
[10-digit phone number]@message.alltel.com
Example: 2125551212@message.alltel.com
[10-digit phone number]@txt.att.net
Example: 2125551212@txt.att.net
For multimedia messages, use [10-digit-number]@mms.att.net
Example: 2125551212@mms.att.net
[10-digit phone number]@myboostmobile.com
Example: 2125551212@myboostmobile.com
[10-digit phone number]@sms.mycricket.com
Example: 1234567890@sms.mycricket.com
For multimedia messages: [10-digit phone number]@mms.mycricket.com
Example: 1234567890@mms.mycricket.com
Nextel (now part of Sprint Nextel)
[10-digit telephone number]@messaging.nextel.com
Example: 7035551234@messaging.nextel.com
Sprint (now Sprint Nextel)
[10-digit phone number]@messaging.sprintpcs.com
Example: 2125551234@messaging.sprintpcs.com
[10-digit phone number]@tmomail.net
Example: 4251234567@tmomail.net
[10-digit phone number]@vtext.com
Example: 5552223333@vtext.com
[10-digit phone number]@vmobl.com
Example: 5551234567@vmobl.com
Other U.S. and Canadian carriers:
Bell Canada: [10-digit-phone-number]@txt.bellmobility.ca
Centennial Wireless: [10-digit-phone-number]@cwemail.com
Cellular South: [10-digit-phone-number]@csouth1.com
Cincinnati Bell: [10-digit-phone-number]@gocbw.com
Metro PCS: [10-digit-phone-number]@mymetropcs.com or [10-digit-phone-number]@metropcs.sms.us
Qwest: [10-digit-phone-number]@qwestmp.com
Rogers: [10-digit-phone-number]@pcs.rogers.com
Suncom: [10-digit-phone-number]@tms.suncom.com
Telus: [10-digit-phone-number]@msg.telus.com
U.S. Cellular: [10-digit-phone-number]@email.uscc.net
Give it a shot!