Sub Sidekick can only provide reliable text messages for one cell phone number and emails for one email address. If you are willing to sacrifice your email alert for another text message alert, then this is possible. But, the speed and reliability of this alternative is not as good. For example, let's say that we have the following two cell phone numbers:

Phone Number (Carrier)
123-123-1234 (AT&T)
321-321-4321 (Verizon)

Look-up your carrier in this list: SMS Gateways. Determine what the email gateway is for your cell phone carrier.

Next, for this example, you would enter in the Alert tab of your Sub Sidekick Settings:
 
Phone Number: 123-123-1234
Email: 3213214321@vtext.com

OR

Phone Number:  321-321-4321
Email: 1231231234@txt.att.net