When running into issues with the same-origin policy, developers implement some of the following methods to bypass these browser restrictions:
Implement a Flash transport layer. In the same way that the server-side proxy works, some developers have used Flash to proxy requests to overcome the limits imposed by the same-origin policy.
Generating iframes to pass data from a source site through to another location where the iframe is loaded.
There are numerous other ways to bypass the issue of communication between sites due to the same-origin policy restrictions, but these are a few of the most commonly implemented.