You don't need a radio operator's license for VFR or IFR (in the US), but you used to. As lifed from the FCC's website:
"On October 26, 1996, the FCC released a Report and Order in WT Docket No. 96-82, FCC 96-421, eliminating the individual licensing requirement for all aircraft operating domestically. This means that you do not need a license to operate a two-way VHF radio, radar, or ELT aboard aircraft operating domestically. All other aircraft radio stations must be licensed by the FCC either individually or by fleet."
Back in the day (before 1996), was it necessary to apply for a radio operators certificate separately from an airman certificate?