ckt diagram is simple just connect pic16f84's serial pin to the mobile directly to Tx and Rx if you are using fbus and if you are using mbus u can connect both pin to single mbus pin on mobile through resistor.
pic Tx --- resistor 220 hms optional ----> Fbus Rx mobile
pic Rx --- resistor 220 hms optional ----> Fbus Tx mobile
pic Tx --- resistor 220 hms ----> mbus mobile
pic Rx --- resistor 220 hms ----> mbus mobile
further more ciruits are given below for pc connectivity
and nokia pins