Not as good as syncing to some online service e.g. Google. I recently bought a new Android phone, before that I used a Windows Phone 8 phone and before that ano

Not as good as syncing to some online service e.g. Google. I recently bought a new Android phone, before that I used a Windows Phone 8 phone and before that another Android. On both the WP8 and second Android, I simply logged into my Google account and all my contacts synced in mere minutes. (On the Android, it also reinstalled all my apps, reconnected to all my WiFi hotspots etc.). I believe a SIM card can hold 100 numbers. Many people will have more numbers than that, so that's not really a viable alternative. Manually exporting to an SD card and then importing (which I believe can be done on Firefox OS, although exporting requires a third party app) is another option, but it's not as convenient as syncing to an online service.