Logical place for reference point is mobile phone – mobile phone is now center of daily activities: you are reachable because of it, you have your contacts, notes, calendars and mails in it. However, no matter how big screen and keyboard are (I am proud owner of Nokia E61), it is useful, for many reasons, to have all those data elsewhere:

• Safety reasons – having a backup of your data is always a good thing
• It is easier to transfer all those data to a new phone; replacing a phone is not very often action, but when you need to do that, it is better to be as painless as possible.
• Easier data manipulation; using “real” keyboard and screen is much more comfortable than using phone
• Access it from anywhere – you can access those data even when your phone is not with you

For years, I am using Plaxo service, which is rather good in free version. “Rather” because I had objections from start of using it:

• It is slow; no matter how new versions are published, beta or not beta, web interface is slow and cumbersome. Response from service is generally “wait for it” and user friendliness is not on high level.
• You need computer, with necessary drivers for cable/bluetooth connection with your mobile phone
• You need to have Microsoft Outlook installed; in the era of GMAIL that is obsolete – you do not want to be tied up for one computer or to worry about licenses.

To be fair enough, most of other mobile phone synchronization solutions are far from perfect; even “native” choice for Nokia phone owners, Nokia PC Suite is generally unusable w/o Outlook installed – way and quality of work with data (over Windows Explorer shell integration) simply can not support any major data changes (even if I disregard fact that this package installs bunch of not wanted software and installs itself in system tray which bugs me additionally ).

I found recently ZYB – perfect “little” web service for mobile phone synchronization. Most of objections above are resolved:

• Service is free with very simple registration procedure; number of supported phone models is very large
• Base for synchronization is SyncML technology, supported by major phone vendors
• Setting up phone (at least for Nokia E61) is trivial – accept and save service SMS sent by site
• Middleman is cut out – no computer / Outlook is needed; communication phone < - > ZYB is direct, using GPRS / 3G / Wireless, whatever is available

First synchronization went fast and almost error free; “almost” because I lost tasks from my phone – tasks are treated as calendar entries; most of phones set up due date when entering tasks and ZYB was setup not to synchronize any calendar items older than 7 days; (I reported this as a bug).

So, please do full backup of your phone using “old way” before experimenting

Apart synchronization, ZYB offers other services – import of address book from Gmail, elimination of duplicate contacts and (unavoidable) social component – to connect with people which phones you have and they are also on ZYB (it is unobtrusive option).

Words of warning: service is still in beta and you can expect some unstabillity; also, there is trust issue – do you want to share your private data with some “foreign” site; I decided that I am fine with that, years ago, when I started using Plaxo service. It is up to you to decide for yourself.

Verdict: My recommendation.