RFID tag and their usage
There are multiple classes of RFID devices. The more legacy devices use a frequency of 13.56 MHz (worldwide) and are operate on the principle of inductive coupling. The range of these devices is typically on the order of a few cm. This is the type of RFID tag that might be implanted in your dog or used for a "smart card" building access.

A second class is called UHF RFID and operates at much higher frequencies. This ranges from 868 MHz (Europe) to 915 (USA) to 960 MHz (Japan) across the global ISM bands. These tags operate on the principle of far-field electromagnetic coupling. These tags are larger (physically about 1/2 wavelength in size) and can operate up to 20m. However, this requires a specialized reader that can output 1W of RF power --- Much more power than a typical mobile phone can generate!!

There are other classes of RFID technology, but I am ignoring them and focusing on the two main technologies.

For the longer range (several m) UHF RFID devices, the process and protocol of being read requires several rounds of exchanges. A reader will tell the tags in view that a round is beginning. Tags will generate a random slot number. The reader will advance through the slots. If the slot matches the tag's chosen slot number, the tag will send an acknowledge. If the reader receives the acknowledge the handshaking will begin, and eventually after a couple more exchanges, the tag will return its identification number. At this point, the tag is considered 'read' and the reader moves on to its next slot or round.

For your project it is difficult to trigger the interrupt when the tag is being read. It would be simpler to use the reader itself. However, there are some chip manufacturers that are using I2C to allow for other sensor data and tag programming. For example, look at the Monza X series: [http://www.impinj.com/Monza_X_Development_Kit.aspx][Link 1]

I think your best bet is going to be:


Use Bluetooth Low Energy (BTLE) instead
Use a reader with a Low Level Reader Protocol (LLRP) link between the reader and the phone
Work with a RFID chip with an I2C bus


EDIT:
[This is a spec sheet][Link 2] for a current chip that cites 20m read range. There have been some improvements since then with regard to lowering the RF sensitivity, but I am not sure what the latest numbers are for this year.

And [one more example][Link 3] from a few years ago showing 100 feet read.

Links: (I don't have enough reputation to link to things it seems)
(1): http://www.impinj.com/Monza_X_Development_Kit.aspx

(2): http://www.impinj.com/Documents/Tag_Chips/Monza_4_Tag_Chip_Datasheet

www.simplyrfid.com/blog/2011/4/20/rfid-read-range-just-how-far-can-an-rfid-tag-read-2011-updat.html