Gathering textible phone numbers is designed to be used with your e-mail client. In order to use the textible phone numbers, you need to have the service provider (AT&T, Verizon, etc) listed. The textible phone numbers are then converted to e-mail addresses using the appropriate information for the listed provider (txt.att.net, vtext.com, etc). Cut or copy the generated addresses into the BCC field of your e-mail client to send.
Also see the tips on the right side of the Gather E-mail and Textibile Phone Numbers dialog for additional help.