NFC operations can generally be categorized in 2 different ways:
Common NFC use
For example, sending a link, or contact, or sending a picture, would be a common NFC use. Its simple, it uses built-in secure functions of NFC to make the data exchange secure (at a most basic level), and NFC devices are usually programmed by default to accept these common uses of NFC technology. This is why you can send a link to an Android phone using NFC, and the Android device understands this. Its an API (or set of common definitions) built into NFC and it works right out of the box.
Secure NFC use
Using your phone as a payment instrument (using your credit or debit cards to pay for things using NFC), and other related NFC uses that require more security than NFC by itself can provide. This requires an additional security element such as a secure SIM. Such secure elements are specifically programmed with additional security information that is also sent via NFC in addition to your credit card or debit card information. This information is verified by the device accepting your NFC information (like a POS), and its this secure element that tells the receiving device that the transaction is valid and should be pushed through.
As of right now, obtaining a secure element or SIM for your phone is heavily dependent on who gives you the device (which in most cases, is your mobile phone carrier). Your carrier has to give you this secure element, and most of them do not do this (yet). NFC is still a very new technology to carriers and mobile phones, so I would not expect to be making mobile payments right out of the box. This requires collaboration between operating system developers (Microsoft, Google, etc.), mobile device carriers and manufacturers (AT&T, Nokia, HTC, Verizon, etc.), and financial institutions (your bank, your creditor, credit card platforms, etc.), and if you haven't already figured it out, is not an easy task.
In regards to using it to access secure areas or opening doors, this will depend on who manages the security infrastructure for your facility, and whether or not they want to support unauthorized devices. It would be a security nightmare if you could simply "copy" your NFC information from one device to another. I can't imagine that this will ever happen, even if its technically possible. Of course, it could be as simple as your company or the company that manages your security developing an app that uses the NFC on phones to allow such use with or without a secure element. Possible, not impossible. Unlikely more than likely.
Keep in mind that I dumbed this down quite a bit, as its far more complicated than just common and secure NFC use, but this is the general state of things, so don't expect miracles anytime soon. Maybe next year.