According to Gaile Gray, ArenaNet Forum Communications Team Lead, during the Free Trial period, Trial Accounts will have several restrictions:
- Trial Accounts can send mail only to a player who has added the trial account holder to their friend list
- Trial Accounts can send whispers only to a player who has added the trial account holder to their friend list
- Trial Accounts cannot use map chat
Here are some other details about trial accounts, and how trial accounts work:
- Those playing on a trial account cannot sell items the Trading Post
- Trial Accounts will be limited to 2 character slots
- Trial Accounts will not have access to the Gem Store
- Trial accounts will not have access to the Currency Exchange
- Trial accounts will have access to Edge of the Mists but will not have access to World-versus-World
Also, FYI: there will be no guild restrictions in place, so your friend playing on a free trial account is welcome to join your guild and will be able to chat and play with you and your guild members.
Source: Official GW2 forum