Just let the service lapse after the 3 month trial period, they will send you a invitation - generally if you don't sign up with them they don't want to lose a potential customer. Usually they will send you a deal like $77 for a year, otherwise it will be a 3 month trial for a certain dollar amount or something like that, usually reasonable. Wait for the $77 offer.
Be careful
Part 1 - they will ask for a credit card - don't give them one, tell them to send you a bill in the mail....
Part 2 - and this is very important, If you choose to sign up for this 1 year service, you need to cancel your service at least 1 month before it ends or they will auto renew it for a big dollar fee as they will cite you were on a $77 'special offer plan' which is 1 year only. Generally they will try to keep you when you are cancelling, tell them you can't afford it anymore, they will most likely try to keep you as a customer, stand firm for the $77 offer again.
I can't tell you how much a pain in the @$$ it can be if you don't call to cancel ahead of time.
I set up a calendar event on my phone and Gmail calendar to email/txt me to remind me to cancel.
Keep in mind that the $77 is before a few fees, so it ends up being something like $90 something after taxes and fees.....
Hope this helps...