If you made a copy of the OTP key at the time you scanned it from Mt. Gox's site, you can add the same key to Google Authenticator (or any OTP app) on another mobile or as a desktop application if needed, using this:
- http://code.google.com/p/cuteauthenticator/
or
- https://github.com/mclamp/JAuth
To keep your backup of the key available online somewhere, you could encrypt it with GPG and store the encrypted version someone where you have access even if your phone is gone. (e.g., if your e-mail also requires OTP authentication and your phone is gone, you aren't getting into that either to get access to your encrypted Mt. Gox OTP key.)
If you haven't made a backup of the key, be prepared to provide identification (again) matching the verification info the exchange has on file, know recent account history, ..., e.g., last deposits and trades, etc.