for local socials it makes sense to call/message people before you go. especially if you go to foreign country/city. for festivals of course you can do it with some people (arrange months ahead that you'll both be there). but to expand your horizons you need to spend time (sometimes days for me) to find these people, befriend them, figure out their dancing preferences, learn names, etc. For me often 1 festival is not enough time to do all that and I need to restart. But I also don't invest too much time, usually couple sentences between dances where I'll mishear or forget answer to questions, etc. In local parties you have not 95% unknown people, but 95% known, so if you match with someone new, you can spend few songs talking to them.
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I don't have good answer to this. I used to ask for the name, connect at FB, then figure out the rest in messages over time, so by next festival I already have some understanding of the person. But now kids use Instagram, FB is abandoned. I'm not sure. Need to ask for phone numbers? (WhatsApp) Americans do that to hook up. I don't feel like exchanging phone numbers with someone I've just met.
In last 2 festivals I did acquire few new favorite dancers where we had many good dances, I approximately remember names. So next time, I'll just say hi! But I didn't get any contact info from them. I can of course ask some common acquaintances.
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sorry for rambling, social skill issues. help.