While Golf League Tracker doesn't have a native way of sending text messages, every major phone provider has a way to send an e-mail to a customer that comes up in their texting application.
For example, if a player uses Verizon for their phone provider, the e-mail address to send them a text message is [phone#]@vtext.com, where you insert their phone number as indicated. So if the player's phone number is 1-248-555-1212, you would email them at email@example.com
Each phone provider has a different address to send to, but most are phonenumber@provider. For a list of the more more common providers, take a look at this list.