The page mentioned is apparently no longer available on the verizon site, but the internet wayback machine archived it:
[Note the part about 2-year contracts....]
What is the Smartphone Port-In Credit?
For a limited time, you can get $150 bill credit* for each 4G LTE smartphone line you switch to Verizon Wireless, America's largest and most reliable 4G LTE Network.
To qualify for the bill credit you must port in your line from another carrier and activate a new 4G LTE smartphone on a 2-year contract or by using Verizon Edge. Shop for the latest smartphones online or visit a Verizon Wireless retail store.
Thanks for contacting. The number was ported on 11thDEC2014. I am pretty sure the promotion was on and was one of the reason for me switiching.
Awaiting your reply.