Regarding the internal GPS on the Samsung Omnia (in my case the original i900):
1. Ensure to connect to the GPS Software port not the GPS Hardware port.
2. Use Franson GpsGate or similar to duplicate the port again
But, generally, I found that the A-GPS sometimes presented very inaccurate positions with (faked) high quality attributes, making it unreliable. Other times, I found the GPS to drain the power of your device so quickly, making it very inpractical. Plus, it generated so much heat in the device.
I found far better results using an alternate GPS (e.g. GlobalSat BT-368 SiRF III Bluetooth GPS) which gave a superior GPS experience but at the expense of needing to carry two devices which required to be charged separately. With the BT-368 I found the ArcPad experience was far more stable and the GPS fixes were faster and the GPS positions were better. If you're going to go down this route, I suggest you search for SiRF III Bluetooth GPS in eBay.