Many android phones doesn't have lots of internal memory storage, normally in the range of 150 to 200 MB on mid range android phone like galaxy ace. But some apps and games like NFS shift and real football only allows you to install on internal memory. As the no. of installed apps increases, obviously phones having inadequate amounts of internal storage gets full. Now even your messages will be rejected due to this problem But here's some tips to free up a few MB on your android's internal storage.
Clear Application cache periodically.
By clearing the cache files of some large application will give you a few megabytes back. The basic way of removing apps cache is by going to Settings > Applications > Manage Applications the select the applications you wants to clear cache then hit clear cache button. Surprisingly only by clearing internet cache , I got around 10 MB internal memory space.
Use Apps to SD
Apps to SD is free and useful tool available on Android market. This software will help you not only by removing the application cache by a single click also helps you in finding applications that can be moved to SD card. Then you can simply move the app to SD using the software.
Remove System Software updates of Youtube, Maps, Market etc,
Google maps is one of the main memory consuming system app on android. By a recent Google maps update I lost around 12 MB of phone memory. Youtube and market updates are significantly large so if you're very tight in memory, remove the updates of these apps by going Settings > Applications > Manage Applications and select the app the uninstall updates.
Try these tips so you can free up significant amount of phone memory on your android device.