VisionMobile writes in the context of the mobile industry:
Customisation (as in handset customisation) is the act of modifying a vanilla handset by the operator to suit the goals of the operator (or in general the service provider). Handset customisation typically involves adding a hard key that leads to the operator WAP portal, changing menus and icons, and branding the handset user interface to promote the operator brand. In that same context, we can talk about service customisation, as in branding the operators WAP portal to use the operators trademark red, orange, blue or magenta colours as a tool to appeal to the operators key demographic.
Personalisation is the exact opposite of customisation. It is the act of modifying the handset or service by the user, to suit the users own needs. Think of changing the wallpaper and ringtones to appeal to the users taste. Or swapping the handset fascia to a bright pink or a solemn black. Or even having the user choose what shortcuts and icons to see displayed on the operator WAP portal, instead of using the operators one-size-fits-all content and branding.