Geez..
It really does not matter what frequency the phone is on.. It is only really limited by the phone's quality. From what I hear, 900mhz allows for the most 'bandwidth' with least amount of interference and most range. But, if you buy a cheap 900mhz phone, you're going to have noise anyway.
Oftentimes, the el-cheapo microphone they put in the phone picks up noise from all over the place. You can fix it (albeit it won't sound as good as a decent phone) by opening it up and putting a thin sponge over the microphone.
Buy yourself a better phone. IMO, General Electric phones are dead worst. Uniden, despite being cheap in price, is fairly decent quality. Even though I hate Sony, their phones seem to work very nice. Also, I would stick with 900mhz since 2.4ghz interferes with wireless networking.
Also, if you want best sound quality and don't care about privacy, get analog. If you want privacy, get digital. Like, if you'd rather hear slight static when you're almost out of range or something is interfering, then get analog. If you would rather just have gaps in the conversation or dropped calls when you're out of range or something is interfering, then get digital.