It’s very likely that you’ll set up an auto-reply message while you’re at a conference or any other business event. What’s more, some of your prospects will be there as well, so you should use an opportunity like that to meet them in person and strengthen that relationship.
My OOO is almost always “I’m out of the office and will be returning on x date.” My email sig has instructions along the lines of “for questions on x, email this list” for a couple of the more common areas people would contact me about that might need an urgent reply (as the lists go to more than just me, obviously), but most people have finally figured out to contact those lists to start with, anyway. If I were in the middle of a project or something that needed to be moved along in my absence, the project teams usually know when we’re out, but I’d put a back up in that case, if needed, but generally there’s not much to be gained by a longer OOO from me.

If you need immediate assistance during my absence, please contact (Contacts Name) at (Contacts Email Address). Otherwise, I will respond to your emails as soon as possible upon my return.
I do enjoy the transcribing of voicemails, so a lot of times I read that (and try to translate the weird interpretation from Siri). I rarely need to actually listen to the voicemail.