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It won't be long into your phone conversations that people discern that you're about to ask for something. The typical response is to start to dodge the issue and create smokescreens for why they just can't attend the training event. The best way around this is to explain that you're calling for the specific purpose of setting up a time to meet with them. That can take the pressure off both them and you. Here's one example (slightly condensed) of how a conversation might go with Katie, a freshman:

"Hi, Katie. This is Stephanie from InterVarsity. Yes, we met a couple of times in the fall after the large-group meetings. Well, as you may or may not be aware, the chapter is planning to attend a training event called Bible and Life next month. . . . Right, Paul talked about it last week. I'm calling you to find out when would be a good time for us to get together so I could share some of the details about the weekend with you. I've blocked out some time between classes next Wednesday and I'm on campus studying Thursday morning. Out of the two, is there a time when we could get together over a soft drink at the student union? Which one of those days would be good for us to meet? Great! And what time is best for you? Okay! See you next Thursday at 9:00 am in the Union. I'm looking forward to getting to know you a little better, Katie. 'Bye!