Which one are the most important? Email or mobile number? I've seen facebook do let user choose either to register to use mobile number or email. Any Ideas?
Currently I'm doing registration for parents and students....
I can't help feeling that if you can't answer this question yourself, then you don't know what you are going to use the data for even when you have it.
Maybe if you think about what data you actually need it might help? Do a little role playing where you put yourself in a position where you actually need to make use of this information in different situations.
Then, let's say for example you're going to put an information box next to the field on the registration form, and in the info box you're going to tell the user why you need the email address or why you need the phone number. What copy would you put in the boxes to make them want to part easily with the information.
Once you have that conversation with your registrants you might find the answer to your question just falls out of the box.
Maybe both are useful. Maybe one is a fallback for the other. Maybe one is good for general notifications and the other is for more urgent contact. Maybe one is for digital contact and the other for human contact. Or maybe you just let your users decide rather than making the decision up front for everyone.
What I'm saying is: given the information available, only you can answer this question for your particular scenario.
Which one is the most important? It depends! No really - it does.
I assume you’re designing a public facing web site, where your target is to let new users register to be able to access content. And you want to decide whether to use Email or phone number when they register. If your goal is to get as many users as possible, my recommendation would be to use both. Some users like to register with their Email address and others there phone number.
The issue here could be that it takes longer to implement two registration channels: SMTP connection and SMS service. But this is a project cost and implementation time problem that is subordinate to the user experience question, in my humble opinion.
Mobile numbers will go away within a couple of years. Email is ageless technology.
The difference is that in most countries a mobile phone number should be linked to a personal ID (passport/security ID, etc.)
In mobile-oriented site or app it could be mindful to auth by phone no., but a user could have no one. Linking to the mobile number, you hard-link your user to a physical device, limiting his/her capabilites to log in without the device / with uncharged battery, etc.
If you're only able to do one, I'd go with email. Mobile number is very personal to a lot of people; they are concerned about spam calls. Sure spam emails are a problem too, but they don't demand time in the same way as a phone call. Also Facebook is a well-known name - providing your phone number to them will be regarded as 'safer' than to a smaller, less-known site.
Keep in mind that depending on the age of the students not all of them will have a mobile number, so you'll either need to allow a phone number (the parents) be used for more than one account or have email as a secondary option. I think the key point you're missing is that facebook lets the user choose if they prefer to use an email address or mobile number.