Folks need to work on providing accurate information before they practice their sarcasm...
The 900 MHz machine in Dallas is in fact a Quantar, which means the digital mode is APCO25. Not sure what the NAC is but I can in fact confirm, without being a jerk, that it is P25. Your only options if you want to use the P25 side is an XTS2500 or an EF Johnson 5100/51 series. Otherwise you can get your kicks with any old analog ham radio or commercial radio.
hamstang you have been given 3 answers, mine probably is incorrect, another reply gave you some printed TRBO listing that correlates with what a local friend told you.
Hope one of our replies helped you out.