It's basically impossible to fly freight as a low-timer, as the majority of the equipment used is single-pilot. In addition operators expect you fly in IMC. Thus the the single-pilot IFR minimums specified in Part 135 apply, and that specifies 1200 hrs.
Cardinal is right on the money. Specifically look at 135.243 (1200 hours, 500 cross country, 100 night, 75 instrument. Some carriers that have aircraft that require 2 crewmembers will take lower time pilots but you better have your &%$# together and they will usually only look at those that will soon meet the mins. for PIC. Quite often it is an insurance issue as well. The carrier may be able to get lower rates for his insurance if he employs more experienced pilots.