Many I know have the 'talk once a week requirement' so if you'd like that your DC certainly wont be the only one! We don't have a regular slot but if I haven't heard for much longer than that I tend(ed) to send a text and only phone them if still no response.
Generally I only got ad hoc communication if something was needed - usually money for sports kit or how to cook something in the student 'kitchen' to feed a dozen mates in 5 minutes time type advice

As they've got older I hear from them more often for a chat. Perhaps it's to do with them having 'proven' their independence or me getting better at not asking too many questions....
Ages old advice is to not let them come home in Freshers term but to go visit them maybe once - after at least a month. It's less unsettling.
For those who are too busy to see parents we found they could usually manage the odd hour if we took them (& a friend or two) out to eat. Obviously depends on how far away you are! On occasion we made it into a weekend break that just included seeing DC rather than expecting to see them very much.