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Overseas Roaming Fees that O2 Charges to Non-UK Phone Providers

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   I live in Japan and have a Japanese phone from NTT Docomo.  When I travel to the UK, I sign up for an overseas data roaming package with NTT Docomo, and I connect automatically to the O2 network when in the UK.  I always keep my iPhone set to use the minimum data:  no background app refresh, no automatic updates unless on WiFi, videos don't run and photos/files don't download automatically unless on WiFi, etc.  I never use video or music streaming and I never download any files unless I'm on WiFi.  

   I was in York for four days in an area which is at best 3G and almost never picks up 4G, and the only things I did on line were to check some emails (no attachments), a little chatting, and Google Maps to get around town.  I was flabbergasted when I returned to Japan to be told that I had used 2.6 Gb of data in just four days in the UK!

  I requested an explanation from NTT Docomo and received a very detailed itemized statement of data usage, with connect times and durations.  To my great surprise, there were eleven items which claimed I had used 104 Mb each, in the space of a few hours.  I was even more surprised that many of these supposed 104 Mb items were for very short connect times, like 5, 3, 2, or even 1.5 minutes!  On a 3G network in York, I don't think it's even possible to download 104 Mb of data in 5 minutes, much less in 2 or 1.5 minutes.  But that's beside the point - the fact is that I never did anything with my phone that would involve a 104 Mb download, and I certainly didn't do it eleven times in a few hours either.

  I complained to NTT Docomo and they agreed to check with O2.  A disappointing answer came back:  "We asked O2 if they had any system irregularities while you were in the UK and they said no".  I have raised a complaint within Japan to take this higher because I believe it's unacceptable for NTT Docomo to allow its customers to be charged amounts like 2.6 Gb in four days when they didn't even use data.    I have even checked Google Maps and it is said to use about 0.67 Mb for every 10 miles plus about 0.78 Mb for every 20 minutes of navigation time.  In all the times I used Google Maps in those four days, the total couldn't be more than 60-70 Mb.

  So what I would like to ask anyone on this forum is the following:

1.  Can you think of any way that O2 would register 104 Mb of data usage in such short times, and repeated so many times in a few hours?  To repeat, I was told I had connected eleven instances in the space of a few hours, and that my connect times were from 1.5 to 20 minutes, often less than 5 minutes, and each time the data amount O2 claims I used was 104 Mb.

2.  Since this is almost definitely a fault, do you think that perhaps all of NTT Docomo's customers have been charged the same way?  In other words, is it possible that O2 and NTT Docomo have an obscure agreement that each time a customer joins the network, O2 can hit them with 104 Mb?  Is there any significance to this number?

3.  Can anyone at O2 direct me to the department in O2 that handles billing for NTT Docomo users?  NTT Docomo has stonewalled me and is refusing to cooperate further with my inquiry, because they claim "there was nothing unusual with O2's system at the time".  I am raising this to equivalent of OfCom in Japan and also plan to raise it to OfCom in the UK as well, as it is a problem which is obviously very unpleasant and costly to any Japanese residents who may subscribe to data roaming while traveling in the UK.

  Please feel free to ask for additional information if you wish.  Also, please no really basic answers like "are you sure you didn't download a huge file eleven times?"  or "are you sure you were really on WiFi?" because I have a reasonable degree of technical proficiency when it comes to managing data usage on my iPhone.  Thanks!


Message 1 of 6

Level 94: Supreme
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Hi @Japan_Jim 

You have posted on a customer to customer forum and I'm unsure as to whether any of us could answer your question in detail as we have no access to your account.


All I can do is give you details of how to contact O2 (please don't use live chat) Guide: How to find help & contact O2 

Also, before you take up any issue with Ofcom in the UK you will need to have followed O2's complaint's procedure


Best of luck with this and welcome, albeit briefly, to the O2 Forum. Welcome

*The Game Is On*

Girl in a jacket
Message 2 of 6

Not applicable


Firstly, I hope you had a nice trip, York is one of my favourite places in the UK.

The only real way to guard against this is to switch off mobile data entirely.

Apps such as WhatsApp work by holding open a connection to the service or frequently connecting to check for messages.

Google Maps will have probably checked for updates to the maps it had stored locally too.


Also a great many apps seem to include a notification function so will install something to run in the background to check with a service, including banking and credit card apps so it can all add up.

Although the original WCDMA UMTS specification's theoretical maximum data throughput is around 384 kbps all of the operators in the UK have deployed the High Speed Packet Access (HSPA+) extensions which boost the throughput to a theoretical 42.2 Mbit/s).


By all means contact O2 but I suspect they'll pass you back to NTT and won't tell you anything about how much they charge NTT because it would be seen as commercially sensitive and whatever they charge NTT will add to it so they make a good profit.


Sorry to be a bit negative and I sincerely hope this experience doesn't stop you coming back to the UK.




Message 3 of 6

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Thanks for the links, Cleoriff.  I actually got a pretty decent response from Techtamer which may have answered my question, so I'll keep looking into the matter and post whatever I may come up with.  

  In any case it's clear that the smartphone manufacturers and Big Tech has fixed things up so all of us use tons and tons of data all the time, usually without even knowing it!  Techtamer's advice of just keeping mobile data OFF - and another suggestion I had which is just keep the damn phone off! - seems to be spot on...


Message 4 of 6

Level 94: Supreme
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If you are only coming over for a few weeks or so, maybe next time just pop into an O2 store and get a Big Bundle sim card. A £15 top up will be far cheaper than the extortionate bill you have probably received from your Japanese network and will be more than adequate for your needs. You can even pick them up at the airport upon your arrival or maybe an International sim to help with the cost of making calls back to Japan.

Have a look at these on the shop page ::


I know this in no way helps with your original query but I hope it helps for future reference.

Message 5 of 6

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Hi there Techtamer,

Thanks for the reply.  Interesting to hear that the system upgrade gives them a theoretical 40+ Mbs, so yes I can see that 104 Mb in 1.5 minutes would be technically possible.  I'm also aware as you point out that many apps query the network randomly.

  However, even with that knowledge, I have never ever used so many megabytes in a day or even in an hour while in Japan.  Typically my usage is 30-60 Mb/day, and what I was doing in the UK is no different to what I do at home.  Therefore, the eleven instances of 104 Mb being supposedly downloaded in very short connect times (1.5 - 9 minutes) over the course of a few hours in one day are very suspicious and indeed completely unprecedented in my mobile experience.

  Since my contract at home is only 2 Gb/month and I almost never use it up, it's very very odd that I would use an entire 1 Gb in less than one day in York.  So while your advice about switching off mobile data entirely is good advice, I'm still interested to hear any view you have on the eleven cases of 104 Mb "usage" on my bill.   Thanks!

Message 6 of 6