This message is both a recommendation and a request for clarification of a very puzzling series of events.
I have a Yallo mobile plan that includes a certain amount of roaming data and call minutes.
Currently I am abroad, and as soon as I left Switzerland I started receiving multiple calls a day from a variety of EU countries (Belgium, Germany, France, the Netherlands, you name it), each call from a different number. As this clearly looked like some kind of coordinated attack, and the numbers were all unknown to me, I just ignored them.
I was assuming that this was some kind of scam involving the network operators of the foreign country. My thinking was as follows: they know that there is a foreign user who joined their network, they know what is their number, and their start calling them from abroad so that they generate traffic and they can profit from whatever cost sharing agreement they have with the foreign operator.
After several days I opened the Yallo app to check my data usage, and I noticed that half of the minutes included in the roaming package had been used, even though I never placed or answered a call during my stay abroad .
I looked into the call log and I saw that all these calls that I had been ignoring were going to voice mail, and each call was being logged as lasting between 5 and 9 minutes.
So, here is the recommendation part: if you go abroad, make sure to disable voicemail to avoid incurring in charges even without using your phone .
Then, the puzzling part comes.
When I deactivated my voicemail, I was expecting that I would still receive the calls, but at least they would not eat into my roaming minutes.
Instead, surprise surprise, the calls stopped . That is, deactivating the voicemail resulted in no more missed calls - they were not trying to call me anymore .
This can only mean one thing: whatever entity orchestrated this swarm of calls, they know my voicemail settings.
This puzzled me. I am not sure what kind of agreements Yallo has with foreign network operators, but I would be surprised if that included whether a user's voicemail is active or not. To the best of my knowledge, only Yallo knows whether a subscriber's voicemail is active. Also, the one entity that has the most to gain from consuming my roaming minutes is Yallo itself, because then they can sell me a beefed up roaming plan or just charge me ridiculous amounts for calls abroad.
These considerations left me with the unpleasant feeling that this is a ploy organized by Yallo to fraud their own customers into buying more expensive plans or generating non-free roaming traffic. On the other hand, I can't believe that a company would try so blatantly to damage their own user base.
So, questions to those who are more knowledgeable that I:
Is it possible that mobile operators share customer details (including voicemail settings) with their roaming partners? If yes, is this a known form of scam organized by some foreign operator? Is there a list of countries/operators that are known to engage in this activity?
Thanks a lot for your help, cheers