It has taken ten years of work, as well as very many instances of mobile users suffering from "bill shock."

But finally this week roaming charges in the EU will, in the main, be no more.

From Thursday, mobile phone users living within the bloc will be able to use their phones as if at home while in other member states, with relatively little concern that they will be hit with massive charges when they get back.

It is not before time.

For years telecom companies have been penalising customers who dared to make a call, send a text or use some data while travelling within the EU.

Now, after a long and tough battle with worried mobile operators that required more than two years of negotiations and U-turns, the deal is sealed and about to take effect.

The plan had been due to kick in at the end of 2015, but was blocked earlier that year by ministers of national governments through the European Council.

So what does all this mean for me?

When it comes to making and receiving calls and sending and receiving texts, the situation is pretty straightforward.

If you have an Irish mobile phone, you will not have to pay anything more than normal charges to make calls to and receive calls from other phones in the EU while you travel within the EU.

The same applies for texts.

So in other words, if you are on a post-pay plan or bundle with an Irish operator that gives you 200 free minutes and 10,000 texts, they can be used for no extra charge in any other EU country provided the calls are coming from or going back to another EU based phone.

If you already have a contract that covers roaming inside the EU, it will automatically be converted to include all your domestic minutes and texts in your roaming allowance.

If you have a contract that lets you roam at preferential rates outside the EU, you can still opt to keep that.

That all seems great. Any catches?

Eh, yes. Quite a few actually.

Data is the big one, but more about that later.

The agreement aims to make life easier for those who travel around Europe occasionally.

According to the EU Commission, it is not meant to be used for permanent roaming.

In other words you must use your phone more at home than abroad in order to meet the "fair usage" criteria.

If you break this condition, then the operator is within its rights to charge you for roaming, capped at 3.2c per minute for voice calls, 1c for each text and €7.70 per GB of data - a figure that will decrease gradually to €2.50 by 2022.

The fair use policies can be imposed by operators provided they are reasonable and proportionate.

OK, seems fair enough I suppose. What's the story with data then?

This is where it gets much more complicated and many would argue, less fair.

The new system is being touted by the EU as "roam like at home", except in reality that doesn't apply to data - the service people use most these days.

After coming under pressure from telecom operators, the EU buckled and put in place rules and limits for roaming data usage.

These are dictated by the type of contract the user has and if the limits are breached, then data roaming surcharges up to that maximum of €7.70 plus VAT per GB will be applied.

This is the current wholesale cost to an EU mobile operator if one of their users incurs data roaming costs on another EU mobile operator's network.

Pre-pay users can use their domestic data allowance while roaming in the EU, provided they currently pay less than €7.70 per GB of data at home.

However, the amount of data that they can use while roaming can be capped by their operator at the level of credit left on their account divided by €7.70 when they first start roaming.

So far so confusing. What about post-pay?

If your operator has not explicitly told you that you have a roaming data limit, you can benefit while travelling in the EU from the full amount of data you have with your domestic contract.

An operator can only apply a "roam like at home" data limit if you have a contract that gives you unlimited data at home or you pay less than €3.85 per GB of data used (a figure that will decrease with time).

The actual limit on the data allowance though depends on the monthly amount you pay for your mobile contract.

The formula is that it has to be at least twice the cost of dividing your monthly bundle cost, excluding VAT, by the €7.70 wholesale cap rate.

So for example, say Joe Bloggs has a mobile bundle including unlimited calls, SMS and 10 GB of data for €30.75 (€25 excluding 23% VAT).

That means he pays €2.50 per GB (€25 divide by 10GB).

So when travelling in the EU he can make unlimited calls and send unlimited SMS, and he will have at least a 6.5 GB data allowance (2x(€25 divided by €7.70) =6.5).

The operator must tell him in advance if such a limit is in place, and when he reaches that limit.

And if he uses more than 6.5 GB while away, his operator can apply a surcharge of, you guessed it, €7.70 plus VAT per GB.

And what about if I get my smartphone as part of my contract?

Just to complicate things further, if you pay for a handset as part of your bundle, that cost is not included when making the data allowance calculation.

In other words, if you pay €55 a month for your calls, text and data bundle (excluding VAT) and that includes €25 a month for the fancy new smartphone you just got, then your roaming data allowance is based on the €30 service fee.

What about people who live close to or cross borders a lot and who jump from network to network regularly?

If you live in one EU country and work in another, you can choose a mobile operator from either and "roam like at home" provided you log on at least once a day to the home network that you have the SIM card from.

It is a similar situation if you live close to a border and your phone automatically and regularly hops back and forth from one network in one country to another in the neighboring one.

As long as you log onto your home network every day, you can roam freely (within the limits of your contract/bundle/pre-pay account).

Are all the networks here planning to live by the new system?

Yes, because technically they have no choice, even though many would prefer not to.

When it comes to data, however, some are opting to offer the minimum fair usage amount, while others are offering more.

Tesco Mobile says it will abide by the "roam like at home" regulations, but customers will only be able to use the fair usage amount of data using the formula above.

Vodafone, on the other hand, will let its customers use their entire domestic data allowance while roaming and on certain plans is offering increased data limits. It is the only Irish operator doing this, although it would probably have to offer close to the domestic allowance in most cases anyway because of its pricing structure.

Meteor/eir will also comply with the EU's rules on roaming, meaning that depending on their tariff, customers will be able to use all or a chunk of their data allowance while traveling in Europe, subject to fair usage policies.

After an attempt to wriggle out of its obligations, Three has rowed back and is now agreeing to live by the plan, again subject to the fair usage policy. That means its All You Can Eat data customers won't be entitled to that full benefit when abroad.

Virgin Media will cap its Unlimited Plan customers at 5.5GB of data allowance when roaming in the EU, while those on the 1GB plan will only be able to use that amount when abroad, in line with their domestic limit.

And Carphone Warehouse owned iD Mobile will abide by the fair usage policy, which will be fair enough for most of its customers, except for those with a 30GB monthly data allowance, who will only be able to use 6.3GB when in another EU country.

Wow, that's a lot of information! Anything else you want to chip in?

Only that if you aren't sure how any aspect of this works, just contact your operator and ask them what your allowance will be.

In any event, they should be telling you around now, if they haven't already.

Plus, they should tell you when you first arrive in the EU country you are visiting and warn you if you are getting close to reaching your allowance.

Comments welcome via Twitter to @willgoodbody