Backup your data on the mobile phone!
How? The easiest way is backup everything with the desktop software. For iPhone you can sync all the data to iTunes software. I suggest do it everyday, just connect your iPhone to the desktop PC iTunes software, click the sync button. At the same time it will charge your phone.
Even old Nokia phones has Nokia PC Suite, or the later version call Nokia OVI Suite (or Nokia Suite). Sony Ericsson has a PC Suite, as well as Android. I have not used the Android PC Suite before.
I bet most normal users who doesn't know how to backup the mobile phone data, do not use any software that I mention above. I suggest to backup to the Internet cloud, I will show you how.
I just choose to backup contact list and photos as an example.
1. Contact (or address book). Link your contact to the Internet, for example Gmail contact. Android is Google friendly, it should automatically sync to Gmail contact.
iPhone contact to Gmail
Connect to gmail using CardDAV. Google has a support page on how iOS sync gmail contact. Different version of iOS may have some minor different in configuration.
iPhone > Settings > Mail, Contacts, Calendars > Add Account... >
Choose any prefer service
Choose an account and follow step by step will do.
Then set Contacts default account to Gmail or the service name you set above (not On My iPhone), so all your new added contact info goes into cloud service and not on local iPhone.
iPhone > Settings > Mail, Contacts, Calendars >
Set default account to Gmail.
2a. Photos to Dropbox. Most users (include Android and iPhone users) should be able to sync photos to Dropbox. You must have a Dropbox account (free register) and you need to connect your phone to a desktop (or notebook to do that).
(iPhone users can turn on iCloud sync in step 2b. You don't need a PC to do that.)
Once you have installed the Dropbox software, connect the phone to the desktop. A screen will display, just click import will do. Select auto import, so your photos will be sync to Dropbox automatically the next time you connect the phone.
2b. iPhone iOS sync to iCloud. You need iOS 5 or later. iOS will sync your photo stream to iCloud automatically when you connect to Wifi.
iPhone > Settings > iCloud > Photo Stream > (set On)
Once activate, you can check your iCloud photo stream from iPhone > Photos > (Photo Stream button at the bottom)
This is just a very brief guide to back up your phone data. Hope it helps you.