Fall Sale: Switch to Verizon and get $100 if you buy a new smartphone (this weekend only)
It doesn't look like the Fall Sale offer is live yet, so Verizon must take the definition of "weekend" literally, meaning just Saturday and Sunday. The offer ends this Sunday, October 23, and requires a new line that must be active at least 6 months. You won't have to pay any activation fee.
If you do port your number to Verizon and buy a new smartphone to qualify for this limited time offer, you won't get $100 in cash. Instead, the money will be given to you as bill credit in 2-3 cycles. Full details should be available at Verizon once you actually purchase a new smartphone and activate a new line (after the offer goes live, of course).