Sony Ericsson W350 is not supported by Apple’s iSync per default, so in order to get W350 iSync compatibility you will need to install a third party plugin.
So far the only suitable plugin I’ve found is the one from Feisar which you can purchase for $3, click here.
This W350 iSync plugin allows you to synchronice using bluetooth. It will synchronize data from your Address Book such as name, addresses, etc. as well as data from iCal including events and to-do’s.
Once you have purchased the plugin, download and install it on your Mac and your iSync is ready to support W350 as if it was done originally by Apple.