I've just made my latest iOS open source project available: JSTokenField
It does it's best to mimic the recipient field in Mail on the iPhone. Tokens will size themselves to fit their titles, rearrange themselves to fit on a line, expand the field as more tokens are added. You can select individual tokens to remove them without having to delete all the ones in front of it. And finally it supports adding entires from the address book.
A token has a title and a represented object. The represented object is simply an 'id' so it can be anything you like. Generally I use a string to hold the number, email address, etc.