Yes, absolutely. There are actually two ways.

1) The application can register itself to handle the NDEF record types it is interested in (NFC Forum well known types, external types, etc.). The details on how to do that are available in the Qt Mobility documentation: http://doc.qt.nokia.com/qtmobility/q...ldmanager.html. This method is NFC-specific.

2) If the record on the tag contains a MIME type, applications registered to handle that MIME type can be launched. For instance if the tag contains a contact card, addressbook is launched by the system because it is known that addressbook handles the contact card MIME type, regardless of whether the data comes in over NFC or some other means.

Depends really on your needs. For just playing around I'd recommend Mifare 1k (which actually has significantly less than 1k of writable memory, something like 750 bytes IIRC) since they are cheap enough and have reasonable amount of space. The smallest Mifares are quite limiting in size, although they can be a bit cheaper.

For commercial use I'd recommend you to contact a vendor that can recommend tags based on what kind of surfaces you plan to attach them on, whether you want them printed with some design elements, etc.