In the meantime, one way to do it that requires some manual setup, would be to have, say, the Ward Executive Secretary build up some email distribution lists (e.g. in his gmail account) for sending out text messages to various groups in the ward. For anyone who has a text-capable phone number, you could save the phone number in the form of an email address. For example, cell phone number 123-456-7890 with ATT&T wireless would be
123456789@txt.att.net; if the carrier was Cricket Wireless the email-to-text address would be
1234567890@sms.mycricket.com; etc. Just google "email-to-text address" for additional references.
For determining who the cell phone carrier is, one way is to enter the number in one of the following websites for example, and it will report who the carrier is:
http://tnid.us
http://www.number-finder.info
Eventually, hopefully the "Send a Text Message" feature will be embedded as an option under "Send a Message" and it will all be handled automatically. But in the meantime, you can do it today by manually building up an email address list(s) using email-to-text addresses.