SMS for gyms and membership clubs
In a membership model, cancellation is the problem, and cancellation starts with people who stop coming. SMS can make that visible early.
The reactivation message
Anyone who has not been in for three weeks gets a short message. Not sales-driven, but personal. People who come back at that moment often renew after all.
Timetable changes
A cancelled class discovered only on arrival is the fastest way to lose somebody. This should go out the same day.
Waiting list for full classes
A place opens up: notify those on the list. This fills places that would otherwise stay empty.
Membership expiry
A reminder a few weeks ahead, with what happens if they do nothing. Clarity reduces arguments later.
What you do not do
Promotions to existing members who have just renewed at a higher rate. People notice, and it costs more than it earns.