The main function of my app:

  • Two users select each other by phone number
  • Neither of them is aware of the other at the beginning
  • Based on certain activities over time, an event happens for both

Due to Hans-Martin Mosner answer, I'm giving more detail.

When user selects another user he writes data to a server in an entry with a certain id. Unless the other user selects that first user so he can now read that id, he's going to be unable to read that data, and for some time, even if it does, nothing is going to display that it has been able to, until some more things happen.

It's true that, theoretically, once the first read happens I would be able to set a new id for the communication, but due to some of the internal data that the entry with the id already would have, and limitations that the server seems to have, I wouldn't be able to do it with a checking done in the server, although I could do it in the client, but this would open for malicious users, with at least a few of knowledge in hacking, to cheat easily with the app.

Server is highly undesired to be changed at this point of development, something that would go a lot against the app expected behavior due to having it would be needed to change it, so if it's not that big of a problem the issue of the phone number I'll have to stick with it, maybe it's also possible that the limitation I'm mentioning doesn't exist, but after a good investigation I haven't been able to get any evidence that, in my case, it could be done, so I want to know how much inconvenience is to expect the inability to keep on working with a changed phone number and take that information into consideration.


If any of the users changes their phone number during the process, my current solution would require both users to start from the beginning, selecting each other again and starting the whole process over.

The only solution to this problem I can think of would make my app far more susceptible to manipulation by malicious users.


I think that changing a phone number is not that usual (I haven't changed mine in my whole life, and I know few people that have changed it in general) so although it can be annoying for some users, maybe the percentage of affected ones is low enough not to worry much.


I'd like to know with trusted data how much of a problem would that be.

4 Answers 4


Learn early

It's sounds like your app is in a pretty early state.
And you are correct that personal numbers don't change much these days.
Now's the time to find out what really matters

If it were my app I'd take a two-pronged approach:

  1. Deploy as is. Users who change their number are going to experience some pain. Make sure they know how to tell you about that pain, and make sure you track the feedback.
  2. Plan for phase two. Start to lay out the plan for how you could address this need. Is there other information you could collect from users to allow them to migrate numbers? Think about the experience and architecture behind that.

You may very well find that it's something you don't have to worry about. But you'll never know until you get it into the wild and start learning from v1.


There's no problem with that. The person who decided to change numbers is aware that he/she will have to add their contacts again, at least the important ones.

If the "migrate contacts" is not one of the functions you're willing to implement in a near future you could notify the users the fact that if they decide to change the number they'll have to add the contacts all over again.

Good luck on your app!

  • Thanks for your answer @Bia, but I'm not sure if you have understood the problem, what I mean is the following: Imagine that both users start at the same time and need to do the operation for 4 weeks, if one of them changes the phone number on the third week, then even if they inmediately started again selecting each other they would need to stay for a whole other 4 weeks, so, in this case, instead of the initial 4 weeks it would have taken, it takes 7.
    – mylket
    Commented Apr 25, 2019 at 16:41
  • Part of the difficulty in understanding your problem is that the problem is described pretty vaguely :-) You probably don't want to share too many secrets about what your app is about, but then people will have to guess what answers might be helpful. Commented Apr 25, 2019 at 19:42

As said in my comment, your problem description is pretty vague and to my understanding contradictory. For example, in the first bullet point you state that users select each other by phone number, but in the second point you state that they are not aware of each other.

If the process of "connecting" takes so long for whatever reason, every user should receive some kind of token when starting, and the app should keep that token even when phone number is changed. Whether this would open up the app for abuse is unclear since proper use of the app is not described...


it sounds exactly like you're legislating for the dreaded 'what-if' scenario.

'What-if' scenarios kill projects dead in the water. Ignore it. It's a fringe use case.

FYI I've changed my number 7 times in last 19 years. You zero.

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