I've just found this program to synchronize the Nokia E71 Calendar with Google Calendar:
http://s60addons.com/calsync/

Its very simple, you just have to install it and setup you google account.

It works in a lot Symbian version: http://www.s60.com/life/s60phones/browseDevices.do?edition=THIRD_EDITION&region=&manufacturer=&sortBy=MANUFACTURER_AND_DATE

ps. If during the instalation a certificate warning appear, you will need to configure te cellphone to install without this verification.

Go in Home -> Instalation -> Mang. aplicat. -> Option -> Config -> Software Instalation -> all

Nice!