You can check the status of your servers using the Exchange Management Shell
[PS] C:>Get-ExchangeServer | fl name,productkey,*trial*
Name : EXCH1
IsExchange2007TrialEdition : False
IsExpiredExchange2007TrialEdition : False
RemainingTrialPeriod : 00:00:00
Name : EXCH2
IsExchange2007TrialEdition : True
IsExpiredExchange2007TrialEdition : False
RemainingTrialPeriod : 119.06:14:51.6643750
To Install product key to a server use the Set-ExchangeServer
[PS] C:>Set-ExchangeServer -Identity EXCH2 -ProductKey 12345-ABCDE-12345-ABCDE-12345
WARNING: The product key has been validated and the product ID has been successfully created. Note: This change will not be complete until the Microsoft Exchange Information Store service has been restarted.
[PS] C:>restart-service MSExchangeIS
WARNING: Waiting for service ‘Microsoft Exchange Information Store (MSExchangeIS)’ to finish stopping…
You can now use Get-ExchangeServer to verify the server is correctly licensed
[PS] C:>Get-ExchangeServer | fl name,productkey,*trial*
Name : EXCH1
IsExchange2007TrialEdition : False
IsExpiredExchange2007TrialEdition : False
RemainingTrialPeriod : 00:00:00
Name : EXCH2
IsExchange2007TrialEdition : False
IsExpiredExchange2007TrialEdition : False
RemainingTrialPeriod : 00:00:00