I'm lukewarm on the subject of tabs. As information organization, they sometimes make sense. You should use special caution when using them on a scroll-and-select device because they might make the rest of the screen difficult to access - getting to something on the fourth tab requires scrolling through the first three tabs, selecting the tab, then knowing to scroll down to get to the rest of the screen.
In a J2ME canvas this isn't too bad, aside from numerous clicks, as you can map left and right to navigate between the tabs and use up and down to navigate the rest of the screen. In a browser page, the user will have to scroll downward to bypass the tabs to interact with the rest of the page (many browsers focus on the top) and I'm not a sophisiticated enough coder to implement tabs without tables or Javascript - both of which are not a good idea on a mobile web page (for now).
The biggest issue with tabs is that they are absolutely limited in how much content they can organize. Even Amazon.com's desktop site has abandoned tabs as its primary organization (one tab is now labeled "all 32 product categories"). On a mobile phone, perhaps 4 tabs can be used if you want to use text labels; only 10 if you want to risk small icons. I wouldn't go for icons unless the user is going to be using the application several times a day, more or less every day - too much to remember otherwise.
Thus tabs as a method of organization are more limited in amount of information than are menus. Their biggest advantage is that you can leave the navigation on the screen at all times. Only sometimes is this desirable for a mobile application because there isn't that much screen available for the application and more content may be more desirable.