ZURICH/MILAN- Rail traffic through the Alps between Switzerland and Italy was halted on Wednesday after an anonymous caller said there was a bomb on a freight train, Swiss police said.The Simplon tunnel was closed at around 11:30 a.m. as police dog handlers searched for explosives. The police said the tunnel might reopen on Wednesday evening.A spokesman for Swiss Rail said buses were taking passengers to the Italian border city of Domodossola.