how can I have an SMS sent from the calendar, or is there something to link the 2 with each other

You will have the option (SMS/eMail etc) when sending an invite for an event added to the calendar.

Send and receive invitations in Calendar on iPhone

1. Tap the event, then tap Edit near the top of the screen.
2. Tap Invitees. If you don't see Invitees, swipe up.
3. Enter the names or email addresses of people you want to invite, or tap. to select Contacts.
4. Tap Done.

Send and receive invitations in Calendar on iPhone - Apple ...