title: How can I use custom fields in a vCard?
body: <p>I'm writing an application which generates vCards from an internal customer database and would like to include additional information in the card, e.g. internal customer number. Reading the RFC, I've see "vendor-specific" extensions, which are to be registered at IANA etc. Are these extensions the way to go? What should I keep in mind while using them, any pitfalls? Are there any alternative ways to define a custom field in a vCard?</p>