If you can't access gmail in your organisation, embedding it in another page is unlikely to avoid this.
Depending on how it is blocked, you may not be able to code any solution to access it.
If you can access your account via POP or IMAP then better than coding anything you could simply to use an alternative mail client (like thunderbird). This might work out of the box, or you could specify the server by IP address (209.85.227.19 should work). That should defeat many naïve web filtering implementations. If you can't access anything outside of port 80 then you could set up your own webmail solution such as SquirrelMail on your own server and use that to access your Gmail IMAP.
Of course the best solution would be to access your personal mail using your own internet connection rather than your work one. Gmail has excellent mobile phone clients, compatable with even the most basic phones, and the built-in mail client on most phones should work well with Gmail.