How exactly should we look at the ministry of Peter, in respect to his calling towards one group of people or another? Acts 15:7 says that his ministry was to the Gentiles, but Paul says that Peter had been entrusted to the circumcized (cf. Gal 2:7)
I would say that Peter's ministry was primarily to the Jews, but not exclusively. After all, he was the one who spoke in the Spirit at Pentecost to men of all nations (cf. Acts 2:14-41). Also, it was to Peter that God gave the vision validating the Gentiles as men worthy of the Gospel (cf. Acts 10:9-16,28; 11:5-10), and it was Peter who converted the household of Cornelius, the first Gentile converts (cf. Acts 10:44-48; 11:15-18). Finally, Peter himself says, at the Council of Jersualem: "Brothers, you know that some time ago God made a choice among you that the Gentiles might hear from my lips the message of the gospel and believe" (Acts 15:7).