How long is a binette really effective?

My fiance and I are expecting a baby on August 23rd. As of now we have a nice sized 2 bedroom apartment in south carolina but we plan on relocating to Washington state in December. In trying to figure out what all to put in the nursery I decided instead of buying a convertible crib/changer combo; to save money and space and just get a binette for the time being. To me it makes more sense b/c we plan on moving anyways within the next 4 months and we can purchase all of that later. Im wondering though; just how long is a binette effective? I've read that they're good up to about 6 months, is this true or not? Will the baby be needing the spaciousness of a crib at 4 months old? Advice please....