Reporter: Tanya Spinka
200 free minutes, 2000 free texts - sounds like a great calling plan. The only catch is that these calls and texts must be made within the same network. So if you know that most of your mates have "021" numbers, or "027" numbers, then you could save yourself a fortune by choosing one of these calling plans. Right?
Well, that's what we all thought until some of us started finding surprise charges on our accounts.
Up to now we've been relying on our friends' phone numbers to tell us what network they're on. So if they're 021 then they're Vodafone, and if they're 027 they must be Telecom. But what we didn't know is that the number doesn't necessarily mean the network.
From April 2007 our mobile providers have allowed us to change phone companies and take our mobile numbers with us. It makes it easier - you don't have to give all your friends a new number, you don't have to change your business cards; everything stays the same. And that's the problem.
Mike Wilson from Waiheke Island got caught out by this in a huge way. He signed up with Vodafone, and on top of all his free Vodafone to Vodafone minutes, he also got a free Best Mate - that's someone else on Vodafone who he could call or text as much as he liked for no extra charge.
Mike signed up his new girlfriend Helen, who had an 021 number. But what Mike didn't know was that Helen's work had switched all their phones over to Telecom. Mike's first month's phone bill? Not the $39.95 he was expecting, but instead a whopping great $281.81.
Both Vodafone and Telecom say that this shouldn't happen; their systems should pick up if a number nominated as a "Best Mate (Vodafone) or a "My Favourite" (Telecom) isn't in fact on their network. They also say that they'll text you to let you know if the person you've nominated changes to another provider after you've signed them up.
Vodafone's agreed to wipe Mike's account, and they say they'll check their system to see if anyone else has been caught out the same way.
If you're on a plan that gives you cheaper calls and texts to the same network, then make sure you check what network your mates are actually on. And ask them before you sign them up as a "Best Mate" or a "Favourite".
If you're unsure what network a number's on, you can text that number to "300" and it will tell you whether the number's on your network or not.
And if your bills are higher than you expect, then check your account. If it says "Off Net" or "Other Network" next to a number you've called, that means the number is not on your network, and chances are you've paid extra to call it.
A new network, "2 Degrees", is entering the market in August. Pricing plans may well change once there's more competition. But in the meantime, check the calling plan that you're on, and make sure that you're not unwittingly paying more than you should.