What is the best cordless phone for a New York City Apartment ?

I know 5.8 GHZ is the best frequency to get. Is there anyone out there who lives in Manhattan, that has a cordless phone that works well when pretty far from the base ? I think that if the phone has an antenna that helps as well, not sure.

Actually, I'd recommend a DECT 6.0 phone. The 6.0 isn't a frequency but rather a standard that had been adopted in Europe some time ago but has just come to the US within the last couple of months. It runs on a new frequency band of 1.9GHz and what makes it different is that it's completely digital, it's completely interference free and it's allocated more power to be used which results in better range. Every DECT phone utilizes frequency sharing techniques which not only checks for the clearest channel, but can tell when other phones/devices are using a channel with a "listen before transmit" feature built into every DECT phone. There are no analog phones or non-DECT 6.0 phones allowed on this new frequency band which makes it the best option. No longer can people's cheap Wal-Mart phones mess you up ;-) 5.8GHz may not be fully utilized yet, but with the availability of cheap 5.8GHz analog phones hogging the spectrum and not incorporating modern frequency sharing anti-interference techniques, it will not be long before it becomes just as bad as 2.4GHz. DECT 6.0 is the way to go for range and to be impervious to interference.

Other nice features DECT 6.0 phones have is that you can associate the handsets to more than one base, and you can use more than one handset at a time on a single base.

Phone range really depends on the construction of the building but will go anywhere from 150 feet to 1500 feet depending. I've noticed some of the expensive commercial DECT 6.0 phones even have repeaters you can set up to extend the range. I think you should at least look into DECT 6.0 options available to you before setting your heart on a 5.8GHz phone.