Dobson Communications Corp.’s $550 million “B” loan has softened to the 99 1/4-99 1/2 range from the 99 3/4 context after Dobson said it will use its $150 million revolver to bid $26 million to acquire RFB Cellular’s Michigan wireless assets. “The guys got a little spooked by this,” one trader said. Lehman Brothers leads the debt, which is priced at LIBOR plus 3 1/4%. Bruce Knooihuizen, executive v.p. and cfo of Dobson, did not return calls.