First you must activate your Google Mail IMAP at your Gmail account.

1. Log in to your Gmail account with your browser.
2. Click on Setting at your account.
3. Click on Forwarding and POP/IMAP.
4. Choose Enable IMAP.
5. Then Save Changes.

Configuring your phone.

1. Open the menu and click on Messages.
2. Click on Email inbox, then Options and Email Accounts.
3. Click on Options, Edit, Now You ready to change the default settings, here we go!!
4. Fill the settings with this value:

• Incoming Mail (IMAP) Server - requires SSL: imap.gmail.com
• Use SSL: Yes
• Port: 993
• Outgoing Mail (SMTP) Server - requires TLS: smtp.gmail.com (use authentication)
• Use Authentication: Yes
• Use STARTTLS: Yes (some clients call this SSL)
• Port: 465 or 587
• Account Name: your full email address (including @gmail.com) Google Apps users, please enter username@your_domain.com
• Email Address: your full Gmail email address (username@gmail.com) Google Apps users, please enter username@your_domain.com
• Password: your Gmail password

• Save your settings changes.

Well done!!!

P.S :

• Please note that if your client does not support SMTP authentication, you won't be able to send mail through your client using your Gmail address.
• Also, if you're having trouble sending mail but you've confirmed that encyrption is active for SMTP in your mail client, try to configure your SMTP server on a different port: 465 or 587.