All monies paid to you (honorarium, travel expenses, hotel reimbursement) is gross taxable income to you and you should expect a 1099-MISC. You can then deduct your expenses and pay tax on the net income, if any.
They can probably "comp" your expenses without tax reporting as long as they aren't paying you money (like comping your conference registration, hotel, and meals). Possibly your airfare. So as long as your only financial benefit is free attendance, it won't be taxable -- either because they don't have to 1099- you, or because the amounts on the 1099-MISC would exactly equal your deductible travel expenses. If you get a speaking fee or honorarium that is more than your actual costs, that will be taxable.
