Yes. In many instances the IRS representative (assuming the taxpayer is in automated collections) will take the information over the phone. In those instances it is not necessary but if they request that the form be faxed over or mailed in, a signature is required. And better be safe than cause delays in reaching a resolution. If you are submitting a 433A or 433B on behalf of a client, their case has usually been assigned to a Revenue Officer and the RO will request that the information be sent to them which requires a signature.