If I get a DECT 6.0 cordless phone, will there be interference between it and the airave??? They both are using the 1.9ghz frequency right?
You shouldn't as the DECT 1.9Ghz phones are on the unlicensed part of the PCS Band, 1910-1930Mhz. This is a portion between the C block uplink and the A band downlink frequencies. The filter in the Airave is decent and should keep noise to a minimum, but if the filtering in the particular model DECT phone you get isn't very good you might experience some issues.
There's alot of cordless phones using 5.8Ghz, you could get one of those to be safe Cordless Phone Search Results | Overstock.com
I've had the best luck using the older 2.4 Ghz cordless phones. They work better in my house than the 5.8.