Want to know if your boyfriend is Mr Right? Not sure what to name your baby? Uncertain whether tomorrow is the best day for Scorpios to plan new projects?

According to the late night TV ads, there's no end to the big life questions that can be quickly and definitively answered by - wait for it - texting your details to 'the number on your screen'.

As harmless and laughable as these SMS services seem to us as adults, to a teenager they can be irresistible. And shockingly expensive.

The same goes for this week's 'must-have' ringtones, phone games and wallpapers.

What many people don't realise is that these are usually subscription services, with your initial text considered as an ongoing agreement to whatever terms and conditions are written in microscopic print below.

That could include receiving a text every week, at around $6.60 a pop, and having to follow an unnecessarily complicated series of steps to unsubscribe, when you finally do catch on.

If your child subscribes to just two of these 'premium SMS services', it could be over $52 a month - before they've even made a call.

Even adults are regularly caught by sneaky premium SMS scams.

Michaela, a world-wise mum, says she responded to an ad on Facebook which read "Are you 43 years old? Enter to win a laptop computer."  (What a coincidence - she was exactly 43!)

After filling out the online entry form, she started receiving phone messages that she thought were just spam, and deleted without reading.

When Michaela's next phone bill arrived, she soon discovered she'd been paying for each message she received.

"I hadn't realised it at the time, but it was all written in the fine print on the ad," she says.

Thankfully, that should all change with a new code of ethics for providers of premium SMS services that has been established by the Australian Communications and Media Authority.

From now on, all SMS providers must be registered, and customers will have to 'double opt-in' - meaning you're told the subscription costs and asked for a second confirmation SMS, so there's no mistaking what you're signing up for. And it will be easier to unsubscribe.

The Mobile Premium Services Code also bans providers advertising to children under 15, and prevents them from continuing to charge for services after the credit on a prepaid account has been used. (Who knew they even did that?)

As of July 2010, you'll also be able to bar premium SMS services on all mobile phone plans. Until then, check whether your phone plan allows you to bar these services and make sure your children know the true costs involved and their own financial limits.

The head of Telstra's consumer segment marketing, Jenny Young, says Telstra already allows customers to bar premium SMS and set spend limits. The company has suspended a number of premium services as a result of unacceptably high escalated complaints and is also introducing a range of new measures to assist customers when using premium services.

A lot of experts suggest a prepaid phone is a good way to limit kids' spending and their vulnerability to subscription services. (Check the fine print though - on some prepaid plans you'll lose your unused credit after 30 days, or if you don't recharge after 60 days.)

While this is great for limiting what your child spends, you still need to consider where they're spending it, especially if they have unrestricted Internet access via their phone.

So far, Apple iPhones are the only mobiles which allow you to put a filter on your child's phone Internet access. Other mobiles don't yet have an Internet filter, so the alternative is to totally block Internet access, which most providers can do.

"Telstra customers are able to activate blocking for Internet access, photo messaging and international roaming for both prepaid and post-paid services if they wish," Ms Young says.

"Parents can activate the service by calling Telstra on 125 111."

In fact, it's a good idea to have a chat with your phone company to check every detail of your child's phone capabilities - as American dad Gregg Christoffersen discovered recently.

The Christoffersens had assumed texting had been disabled from their 13-year-old daughter Dena's phone. Naturally enough, they didn't have it included on their plan. It turns out young Dena could send texts - about 10,000 of them in a month in fact - and was charged for every one she sent and received! ($US4,756.25, thank you very much.)

Needless to say, poor Dena's phone is now permanently out of action, which is a shame because there are lots of good reasons kids might have a mobile phone.

Once again, as parents we need to remember that the cost of all this wonderful technology is simply for us to become well-informed and communicate the rules clearly to our kids.