For most people, holiday roaming warnings kick in when you cross a border. You land in Spain, Turkey, or Morocco, your phone pings, and the familiar message appears telling you to watch your data usage. What almost nobody expects is to get hit with international roaming charges without ever leaving their own country. roaming charges on ferries

That is exactly what happened to Joanne Williams, a Shetland islander who was left staring at a mobile bill nearly £140 higher than expected after her teenage daughter used her phone on a ferry from Shetland to Aberdeen. No passport. No foreign country. Just a domestic ferry journey entirely within UK waters.

And yet, the charges were real.

How a domestic ferry became an international roaming trap

The charges appeared on a bill from iD Mobile and initially made no sense. Joanne Williams only realised what had happened when she lined up the spike in usage with the date of the NorthLink ferry crossing.

The journey between Shetland and Aberdeen is a lifeline route, not a luxury cruise. It connects island communities to the mainland and is treated as essential public transport. From a customer perspective, there is nothing about this journey that feels international.

As Joanne put it, she did not cross borders, did not leave the UK, and did not do anything that would normally trigger roaming precautions. She was not travelling abroad. She was travelling home.

Yet her daughter’s phone connected to a network at sea and started generating international roaming charges.

Why does this happen at sea, even in UK waters

Here is the uncomfortable truth many travellers never hear until it is too late. When you are at sea, your phone often cannot connect to normal land-based mobile masts. Instead, it looks for any available signal and frequently latches onto an onboard maritime network.

These onboard networks are usually satellite-based. They are not part of your standard UK allowance. They are not part of EU roaming. They are not cheap.

From a technical standpoint, your phone is no longer using a terrestrial UK network. It is using a satellite provider that bills at premium rates. The billing system does not care whether you are in international waters or domestic waters. It only cares about how the signal is delivered.

This is why roaming charges can appear on ferries, cruise ships, and even sometimes near coastlines.

Why passengers feel misled

From a consumer perspective, the frustration is understandable. A lifeline ferry operating entirely within UK territory does not intuitively feel like a roaming risk.

Joanne Williams summed it up clearly. If she were flying abroad or heading to a foreign destination, she would have taken precautions. But travelling from Shetland to Aberdeen does not feel like leaving the country because it is not.

This gap between technical reality and customer expectation is where the real problem sits.

Political pressure and regulatory attention

The issue has now gone beyond one household bill. Alistair Carmichael, MP for Orkney and Shetland, has written to Ofcom demanding answers.

His argument is straightforward. Charging international roaming rates on a domestic ferry route is difficult to justify in principle, regardless of the technical explanation. Passengers reasonably expect their mobile usage to behave like normal UK usage on a UK route.

NorthLink itself has not been blamed. The operator has already taken steps to warn passengers and provide guidance. But warnings alone do not solve the underlying issue.

What mobile operators say

iD Mobile confirmed that Joanne Williams received a partial refund as a gesture of goodwill, around £100, but not the full amount. Their advice to customers is clear but revealing.

They recommend switching phones to airplane mode while at sea and setting spending caps in advance. They explain that onboard networks rely on satellite connections, which are significantly more expensive to operate and therefore excluded from standard plans.

This position is not unique to iD Mobile. It reflects an industry-wide approach.

This is not just an iD Mobile problem

Other UK networks follow similar rules. Whether you are with Vodafone, EE, O2, or Three, maritime and satellite roaming is usually excluded from inclusive allowances.

Some operators are better at proactive warnings than others. Some send clearer text alerts when a phone connects to a maritime network. Some do not. But the underlying pricing model is largely the same across the market.

Cruise ship passengers have been dealing with this for years. What is changing now is that ferry passengers on short, domestic routes are increasingly exposed to the same risk.

Why does this matter more before the holidays?

Holiday periods amplify this problem. Ferries are full of tourists, families, and younger travellers who are constantly online. Streaming, social media, messaging apps, and background app updates all consume data silently.

Teenagers are particularly vulnerable. A phone left unlocked with data enabled can rack up charges quickly without anyone realising until the bill arrives.

For island communities, this is not an occasional holiday issue. It is a recurring risk on essential travel routes.

How does this compare with newer connectivity options

This is where broader market trends matter. Traditional mobile plans were never designed for seamless connectivity at sea. They are built around land-based networks.

Newer solutions are starting to change that. Some ferry operators are improving onboard Wi-Fi, although the quality varies. Some travellers now rely on offline modes, downloaded content, or strict data controls.

eSIM providers are also reshaping expectations, but even here, satellite connectivity remains a blind spot. Most consumer eSIMs also exclude maritime networks unless explicitly stated.

The industry trend is clear. Connectivity is becoming global, but satellite roaming pricing has not yet caught up with consumer expectations of fairness and transparency.

What passengers can realistically do right now?

Until regulation or pricing models change, passengers need to protect themselves.

Switching to airplane mode at sea is the safest option. Enabling Wi-Fi only, with mobile data disabled, reduces risk. Spending caps should be set, even on domestic plans. Data roaming should not be assumed safe just because you are in the same country.

Most importantly, travellers should not rely on geography to determine roaming risk. Network type matters more than borders.

Conclusion: this is a warning, not a loophole

The story of Joanne Williams is not about a technical glitch or a one-off billing error. It exposes a structural disconnect between how mobile networks operate and how travellers think about connectivity.

As long as satellite networks are treated as premium roaming zones, domestic ferry passengers will remain vulnerable. This is not unique to Shetland. Similar risks exist on ferries across Europe, coastal routes, and island connections worldwide.

Regulators like Ofcom now face a choice. Either push for clearer consumer protections and transparency, or accept that essential transport routes come with hidden digital costs.

For travellers, the takeaway is uncomfortable but necessary. Before the holidays, before boarding a ferry, and before handing a phone to a child, assume that the sea changes the rules.

Connectivity at sea is not domestic. It is not intuitive. And until the industry evolves, the safest defence is awareness, not trust.