It will be a bumpy ride for the Google Phone, details of which are expected to be unveiled next week, and while expectations abound, Google Phone fans should be ready for a sub-par experience, at least initially, experts say.

For one thing the operating system is immature, Nomura analyst Richard Windsor said Friday in a report, so it could be 12 to 18 months before Android is up to the performance standards of Symbian andWindows Mobile.

Also, the phone will debut on T-Mobile USA’s network, which analyst Joe Nordgaard said will present bandwidth challenges throughout its coverage area, which will give users distinctly different experiences depending on location.

“Whether it’s Wi-Fi or 3G, users will move from fairly good broadband to fairly poor narrowband,” said Mr. Nordgaard, director of wireless consulting firm Spectral Advantage. “T-Mobile is working hard to rollout 3G, but for users, coverage quality will be inconsistent.”

Mobile application performance can be poor because of the challenges involved with hardware and software configuration, phone processing power, and spotty network performance. But adding an untested operating system to the list could add significantly to the performance challenge.

Both analysts cheer Google’s entry into the mobile sphere as important and stimulating, but both believe that the user experience will be disappointing,  particularly to Google fans.

“The iPhone and other smartphones, and the availabilityof location-based services have set the expectation bar very high for Google and while Google has its own high standards, there will be challenges,” Mr.Nordgaard said.

For phone makers and carriers, the adjustment to mobile broadband has not been very smooth. Apple has had a number of problems with the performance of the iPhone 3G. But Apple’s problems may have more to do with the phone’s radio software than the operating system.

“In (Android’s) case…it is the operating system, middleware, applications framework and even the applications themselves that are immature,” Mr. Windsor wrote. “The user experience will not be good enough to really allow Google to fulfill its dreams in mobile anytime soon.”