We haven't enhanced gmail-mobile for a long time. It seems that different phones have different compatibility and tolerability to the standard. So it works here but not there (hardware-dependent), some times but not the other (content-dependent). Some people found it works great, some simply couldn't see even the login page.
This, unfortunately, makes gmail-mobile very hard to debug, to work universally, and to improve.
So, if you are familiar with WML and are interested in developing gmail-mobile, please let us know. Any comments are welcome!