"かまいません" is polite way of saying, while "俺" is not polite. So the first one sounds a bit strange to me.
These probably work well. But if you want to mean "Please don't hesitate to talk to me.", the following is more natural, I think.
When you want to talk to someone, you probably say to him/her "Excuse me", "Hello", "Hi" or something at first.
"声をかける" directly means these first saying.
But after that, you will start business talk, gossip, asking questions and so on. "声をかける" often implies these purposes. It depends on the context.