All you need to do is match the voltage (220V) and the current (miliamps - you want the same or more mA on your new adapter) on the adapter and you are good to go. Many new phones come with a universal adapter - check to make sure if that's the case (it'll say 100-240V, ~50-60 Hz). Then you're good to go and all you need is a surge protector and a travel adapter for the plugs.

Frequency-wise, AFAIK 2.4 and 5.8 Ghz phones are legal everywhere.

Be aware though, that if you buy a DECT cordless phone abroad, as of Oct 2005 it has become legal to use without paying fees but it may still interfere with GSM cell phones operating on the 1900Mhz band.