Fax type question

[abooker]

Apologies, not sure if this was the right place - but had to ask it somewhere !
I'm looking a buying a new Panasonic or Philips fax machine but want to add some more DECT handsets as well, perhaps up to 6. Question: will any DECT phone work with the one on the fax machine ? Do they have to be GAP compatible etc ?? I can't find any info on any of the manufacturers websites so hopefully someone here can help ...
Many thanks in advance

[rct]

GAP compatible is necessary for it to work, but bear in mind that GAP specifies only the ability to make and anwer calls. Menus hardly ever work and even Caller Display isn't always passed.