We have our mobile on Woolies mobile, even though I used to work for their telco wholesaler. Saving 10% off the groceries once a month in store is a no brainer, and we tend to do one big grocery shop a month, which makes the mobile fundamentally free... or, 10% cheaper groceries.
Yep, getting thins aligned like this can work, although there's certainly some that don't...but are presented as being better value.