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I have a web app that you can currently log into with either your email address or your username.

I'm developing a mobile application and I'm just wondering if I should offer the ability to log in with your phone number. If this is the case, a user would first have to provide the service with a number.

I find it convenient on other services I use where I might not remember what email I have connected to it.

Is this a good idea? Would you offer it in a service you were building? I'm trying to decide if its worth the trouble to build.

NOTE: This number would strictly be used for authentication.

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On the security side of things I would recommend one-way hashing the phone number so you don't have a list of people's phone numbers in your database, unless for some reason you need to recall the exact number (don't make it the only identifier for the account, even if it's the only way they login). Security and trust are the only issues I can think of here, usability-wise it can make things much easier, if people trust you enough to use it. –  Ben Brocka Sep 21 '11 at 13:11

6 Answers 6

I would support the use of phone numbers for logging in.

For one its far easier to type in a phone number on a phone than to type in an email address.

Usually a phone is used only by one person so you could even bind an account to a phone if required. (True for most phones that users will be using apps on)

You may want to provide an option to let the user enter a phone number or an email address on their mobile phone, because some users may not want to give you their phone number and some others may get confused when accessing your service/app if they switch between the desktop and phone version.

Caveats:

I know people who dont remember their own phone number at times. (They are not old or technologically challenged in any way)

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It's unusual, but it seems like a good way to get a user name that is truly memorable to the person and unique. A couple of caveats:

  1. Make sure people understand that the phone number is being used as an easy to remember identity and that you won't share it or use it in any other way. I really liked Ben Brocka's comment about storing the number to avoid holding a big list of phone numbers.

  2. Do some sensible chunking of the submitted number so people can detect errors more easily. In other words, instead of a flat string like 5555551212, display as 555-555-1212.

  3. Finally, make this a viable alternative as opposed to a must-do. Some people will probably feel better with an ID or email they're used to using.

I would stay mindful of ChrisF's and JohnGB's answers as well: is the benefit clearly worth the cost? Is this a true improvement or a nice to have?

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Does the functionality of your app (excluding signing in) improve with having a phone number? Is it actually used in the application?

If it is, then it may be worth adding this (WhatsApp is a good example where they phone number is central to the app), but if not then it is probably not worth the added effort and complexity that it adds to the app.

What aren't you improving on with the time you spend doing this? Would the app be better with phone number sign-on or with some alternative improvement?

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It is as valid as a email address or random username. This applies both ways - it is as good as these, but it needs to be as secure as these, so verify on sign up, and ensure a good password.

So I am all for this idea - my mobile provider site uses this - but don't treat it as a shortcut ( especially if you extract the number from the phone itself )

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Would you also be testing whether they string of digits they enter actually belongs to them (eg. sending an SMS/Text for account creation validation, in lieu of the usual email loop) ?

If not, how would the string of digits they enter be any different from a string of characters they enter into a "username" field?

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the app could possibly get it from the phone itself...? –  Marjan Venema Sep 21 '11 at 6:17
    
Possibly, depending on the device API. Also, if this is an app inside a telco walled garden then the network could provide the number. –  Erics Sep 22 '11 at 1:44

I think you've answered your own question.

You state that you find the facility convenient on other services and given that you're providing mobile access it's a logical facility to provide.

The only thing to check is whether it will cost you more to build than the benefit you get from it. However, only you can answer that as only you know your costs and the potential profit you'll get.

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