I'm not sure what the use for the 800/900 MHz would be (business, office security, personal, public safety, farm, etc.) but if it's for a small/on-site coverage area, I would highly encourage the Motorola DTR series radios. They are (VSELP) digital voice, frequency hopping radios that are secure (for the most part) and no license from the FCC is required. They operate on the 902-928 MHz frequency band, and have virtually no interference whatsoever from other devices. The audio clarity is crystal clear, and if you are out of range from another radio, you will get a warning that you are out of range from the radio.
Here is an audio sample I made with DTR radios about 10 years ago:
http://www.w2sjw.com/sounds/Moto_DTR.mp3
Here is the spec sheet for the DTR radios:
DTR700 Digital Two Way Radio - Motorola Solutions
The older model DTR radios would be the DTR 410, 550, 650 series radios. They work well, and you might be able to find some at a discount. The 410 model has a fixed antenna on it, while the 550 and 650 have a removable antenna in case you need that feature.