How old is your site - twentyten has been updated along the way to maintain compatibility with WP core and enable various new features and possibly fix any security issues. So that might be an issue. Or not.
There are a lot of variables so it's really a process of elimination to try to narrow down possible causes of problems like this. The first standard troubleshooting steps are to deactivate all plugins and switch to a current default theme - twentytwelve. Then see if you still have the issue on your phone. If not, reverse the steps one by one to see when the problem re-occurs.