No, unfortunately not. In order to be able to view and edit that shared itinerary, the itinerary 'owner' (ie. the person who invited you to collaborate) will either need to:
upgrade their free 'Trip' plan to a 'Trip+' plan; or
contact us directly giving us their explicit consent to transfer ownership of that specific itinerary to you permanently. You would also need to have a 'Trip+' plan if you wanted to have 'Trip+' plan features such as collaboration, attachments and budgeting.
If the owner of your trip doesn't want to upgrade, but someone else in the trip is happy to, please ask the owner to contact support via our chat widget so we can discuss moving ownership of the trip.