He was out of work for three months与He has been out of work

was(were)done:一般过去时的被动语态.xxx is completed.
他是在三个月前被解雇的.（过去已经完成的）
has(have) been done:现在完成时的被动语态.xxx has been completed.
他已经被解雇三个月了.（现在,还在持续）