If you treat the PDA as simply a display, then you can change your way of thinking about what data actually needs to be sent. It only needs a single trace of data, the width of the display, up to 30 times per second. If we assume 8 bit samples, and a retina display width of 960 columns, then you only need to send 960 bytes 30 times a second, or 28.8kbytes per second. If you are fine with 10Hz update rates, then the link only needs to handle 9,600 bytes per second. When the user zooms in, or changes any of the parameters of the measurement, send the new parameters to the microcontroller, and have the microcontroller prepare the data so you only need a low data rate stream to display the data.
If you want to do analysis on the PDA, then you'll have to send a whole chunk of data, and that's simply going to be slow.
But the more analysis you do on the microcontroller side, the less data you have to send, and the more frequently you can update the display.
Keep in mind that fast bluetooth data links will not connect to iOS devices (iPod touch, iPhone, iPad) without fulfilling the requirements of the Apple Made For iPod program, or jailbreaking the iOS device. This is why many similar devices are using wifi.
If you cannot reduce your data rate, and need the PDA to have full access to all the data with no breaks, you should skip bluetooth entirely and use wifi. Inexpensive wifi adaptors might only handle low data rates, but there are wifi modules that will provide more bandwidth.
This easiest way to do this is to buy a bluetooth module which has serial port profile built-in to its firmware (Roving networks/ panasonic etc have such modules). Assuming your "device" has a microcontroller, the microcontroller could communicate to the BT module via some communication interface (say UART) to transmit and receive data. At the mobile phone end, you need to write an App which will connect and pair with the BT module in your device and once it establishes a stream, your App can transmit and receive data with your device.
This is quite straightforward, I was able to do this and transfer files from my device to an android phone in a week of tinkering.
Best Answer
That should be very easy with an Arduino + NFC (or RFID) reader/shield + Bluetooth module/shield.
Here is a cheap NFC reader (based on the MFRC522 chip) from ebay ~$6 link and it uses SPI for communication, also here is a blog post that shows how to use it with an arduino link
for the bluetooth, the easiest way is to use a serial module like this ~$5 just google "arduino + HC-06" and you will find many results showing how to use it.
then you need to write the code that read data from SPI and sends it over serial.
Update:
here is another NFC reader (based on the same chip MFRC522) link but the module exposes the serial pins UART instead of SPI, so technically you can wire this directly to the bluetooth module (RX-->TX and TX-->RX) but you need to match the baudrate and other serial settings between the two
Some bluetooth modules can be programmed over serial (simple commands to change default settings like Name, PIN code and speed) but i have used one that didn't allow me to change default speed (9600).
also check to make sure voltages match 5v or 3.3v or use something like a voltage divider.