Mobile phone plans and pre-paid deals vary hugely in price and features, which makes it hard to compare apples with apples.

Nor is there a one-size-fits-all deal. A university student may be umbilically attached to his or her phone, whereas someone who works from home may use it infrequently.

Nor are the plans all equal. They have wildly differing caps for texts, calls and data. A free phone might be your bottom line. Another customer may like unlimited Australian call minutes.

You may eat vast quantities of texts/minutes/data, or virtually none at all. Rollover could be a real life saver, or of no interest to you.

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Like me you may feel anxious at the idea of chewing up expensive minutes or megabytes when your allocation runs out so you want a package that stops you in your tracks straight away.

If you travel a lot you may benefit from $5 a day roaming in Australia or cheap deals to other countries.

You may want your children or partner to share your plan. Even if you don't do the sharing thing, many packages offer free calls to others signed up with the same company, which might be good if you call your partner, kids, work or best mate a lot.

Assumption really is the bogey man when it comes to spending less on mobile phones. You need to do your numbers and work out how many texts, minutes and gigabytes you use in real life each month.

Over and above those factors, getting the best deal is most likely to happen through behavioural change. Go back to basics and question your needs to see if you can slice and dice them differently.

One big change in behaviour is to accept that "free" phones are
eye-wateringly expensive. Don't kid yourself the phone is free. It costs hundreds of dollars more to buy a top of the range phone such as an iPhone 7 on a free deal than if you bought the same device yourself and signed up for a better value package.

When I Googled "free iPhone 7 plan", the first result was for Vodafone, at $112 a month for 24 months on a Red+ Lite open term plan. That adds up to almost $2700 over the two years.

If I was to buy that same phone full price at $1499 from Noel Leeming and use it with my existing pre-pay combo, which has everything I need, the entire shebang would cost me a fraction more than $1900 for the two years.

That's a huge saving.

The big problem with "free" phones is that to qualify you have to choose a more expensive plan than someone with the same habits would pay on a pre-pay combo that renews automatically.

This brings me to my next behavioural change point. Much of the data eaten up by smartphones is used up by the updating of apps in the background.

This can be done for free on Wi-Fi. By restricting "background data" on an Android phone or "app refresh" on an iPhone your consumption will reduce significantly,

My own behaviour changed when I realised my 150 minutes a month included calls to New Zealand and Australia. I took note and switched to making Australian calls from my mobile instead of my landline.

One big behavioural change that can really pay off is to quit thinking you must stick to either a plan or a pre-pay.

Pre-pay no longer means a trip the dairy to top up $10 at a time, or even topping up manually at all. Modern pre-pay deals involve combos, which renew automatically each month. Your account is credited by direct debit so it's seamless and makes it as convenient as an on-account plan, but cheaper because the provider doesn't have to take a credit risk on you, and gets paid upfront each month.

To return to plans where the family can share calls and data, I've crunched the numbers and these tend to be more about convenience than money.

Mobile phone plans offer many teachable moments for financial literacy and if you don't want to bring up kidults who never grow up financially, give them a limit.

Allowing children to suck unlimited calls or data from the parental bill is sending bad messages to the younger generation.

The $9 or $16 Skinny 28-day combos are great for this because they teach children to budget their data and calls, but they can still text in emergencies.