EE, O2, Three, and Vodafone will each be required to provide guaranteed phone and text coverage to 90% of the UK, in geographical terms, by the end of 2017.
The deal, initially agreed between the Government and the four UK mobile network operators (MNOs) in December 2014, was made official last week when Ofcom amended the operators' licenses.
Once rolled out, Ofcom estimates the increased coverage should reduce the geographical area with no mobile call coverage by about two thirds.
Meanwhile the area with coverage from some but not all MNOs should be halved.
It's thought the total costs the operators will incur for this work will be in the region of £5 billion.
Around 85% of residential and small business premises are fully served with 3G coverage from all four MNOs, but the geographical coverage is much worse, and varies greatly between 2G and 3G networks.
In fact, geographically speaking, only 26% of the UK has 3G service from all four MNOs.
To add to this, 2G, the older network technology still being used for voice calls, has much better geographic coverage:
SOURCE: Ofcom, Infrastructure Report 2014.
The networks are allowed to factor this older 2G infrastructure into their quotas for voice call coverage.
Combined with the problems providers are facing getting voice calls to work on 4G, this deal isn't likely to prompt a huge jump in 3G and 4G availability.
Another factor that will dampen the effect of the deal is recent talks of industry consolidation.
With Three and O2 expected to merge, and BT due to buy EE, the operators will be allowed to merge their coverage areas and therefore reduce the need for the individual networks to increase infrastructure.
Vodafone will be facing the coverage increase alone, but won't be too concerned. It's already at 82% geographic coverage with its 2G network, just 8% shy of the level required by Ofcom.
Ofcom have found [pdf] 28% of people in remote rural areas don't have any signal or reception on a daily basis.
SOURCE: Ofcom, Consumer experiences of mobile phone calls.
With a third of people in rural areas unhappy with the service they currently receive, and the above-mentioned possibility that deals and mergers could have an effect on how much work the MNOs need to do to meet the 90% requirement, many will see little cause for celebration.
But this deal isn't the only way in which Ofcom and the Government are trying to improve mobile phone coverage.
Ofcom had already set out guidelines for EE, Three, O2 and Vodafone to provide 3G coverage to 90% of UK homes by June 2013, with which all complied.
But the regulator also publishes data designed to promote competition between the networks by highlighting areas in need of improvement, and encouraging better quality of mobile phone services.
The Government is spending £150 million on infrastructure to increase mobile coverage, including voice services for up to 60,000 premises previously not covered, in work due to be completed by 2016.
Additionally the Department for Transport (DfT) and Network Rail are working together to increase mobile broadband coverage, with the DfT investing £53 million to increase Wi-fi access on trains.
In a separate agreement, O2's 4G licence requires it to cover at least 98% of the indoor UK population by the end of 2017 - which should also result in 99% population coverage outdoors.
Note however this refers to population coverage, not geographical coverage. That's likely to be much lower, as in the case of 2G and 3G coverage.
EE, Three and Vodafone have all indicated they intend to match this requirement by the end of 2015, which should have the added bonus of extending mobile broadband coverage to many areas not reached by 3G.
But targets for 4G coverage have a tendency to shift. EE promised 70% 4G indoor population coverage by 2013, increasing to 98% by 2014 - but then revised this to 90% by 2014.
At the start of 2015, EE's 4G coverage stands at 80% of the UK. Vodafone, Three and O2 have 4G coverage of 50%, 48% and 45%, respectively.
Vodafone's Jeroen Hoencamp is unapologetic about the provider's much lower coverage figures, insisting the network is "doing it right first time".
And remember, as alluded to above, 4G does not yet support voice calls - although EE is investing in Voice over LTE (VoLTE) technology which, as it's introduced in the coming years, will enable voice calls on 4G networks.
Another benefit of 4G is that the low frequency at which it operates (800MHz) travels well long distance - a feature important for coverage in rural areas.
Before all four MNOs agreed to up their mobile phone and text coverage to 90%, there were a few other options on the cards
The first was national roaming, whereby people unable to access their normal network could automatically roam to another operator to make a call.
The second was increased sharing of infrastructure, allowing operators to attach their equipment to other MNO's masts.
The third was aimed at mobile virtual network operators (MVNOs) - networks that piggyback off the main networks. This option would have seen them offering mobiles that could access all four networks. If one operator's coverage dropped out, people would automatically be switched to another.
It's not really a surprise, then, that the MNOs chose the option that was by far the most beneficial to them. They get to choose the most efficient, cheapest, combination of options to increase their coverage.
Widespread increases in infrastructure aren't the only ways networks can increase their coverage.
Coverage can also be increased by femtocells - small, low powered, base stations which improve coverage in the home and operate via fixed broadband. Femtocells are offered by Vodafone, Three and EE.
They could be especially useful in open, rural areas. The Open Sure Signal femtocells provided by Vodafone can be installed in any area with a fixed connection, including shops and telegraph poles.
Another option is to install repeaters, devices that amplify weak mobile signals - but these can cause interference, and are at present subject to strict licensing rules.
Despite this, Ofcom is reviewing whether the public should be able to use them with fewer restrictions.
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