**I HAVE ONLY DONE THIS ON THE ZTE SCORE!!! IF YOU DELETE ANY OF THE FILES I NAME HERE ON ANY OTHER DEVICE, OR SIMILAR NAMED FILES, YOU'RE DOING IT AT YOUR OWN RISK!!!
Like many others, I have delt with the "internal storage is low!" issue. It wasn't Apps, Messages, or Browser Cashe. The issue is system logs and/or error reports mounting up and the phone not deleting them for whatever reason. I read other threads about this problem and found that to stop the problem you have to access the phones system files and manually delete the accruing files. These are the steps I took on my ZTE Score.
1) You will need to "Root" your ZTE Score; here is the tutorial I used to root my phone:
How to Root the Cricket ZTE Score X500 - TheUnlockrTheUnlockr
2) On your phone, go to Google Play *if yours still says Android Market, upgrade when prompted*, and download the following apps:
Disk Usage from Ivan Volosyuk
Root Browser Lite from JRummy Apps Inc.
3) Now, the files on my phone that were growing too large were located in /data/adb in my phones internal storage. You need to view the files and confirm if this is your issue as well.
4) Open Disk Usage, under "View" select "[Root Required]", then select "/data"
5) A visual interface will be showing now; in the middle column look for a folder/a blue box, named "adb". It's inside this folder where I found the files growing out of control. They all started with the name "adb" and behind it the date the file was created. Ex: "adb-2012-8-26..."
Nothing more than simple .txt files filled with numbers and dates.
**IF YOU DON'T SEE THE FILES I'VE MENTION AT THIS POINT OR THE FOLDER ISN'T TAKING UP MG OF SPACE, YOU'RE OWN YOUR OWN FROM HERE TO FIND THE RIGHT FILES; YOU'RE DELETING AT YOUR OWN RISK!
6) Now that the problem files have been identified, open Root Browser Lite and use this app to delete them. Select the folder "data", then the folder "adb".
7) Once inside the "adb" folder, select "Multi-Sel" in the bottom task bar, then "Select" in the task bar that will now appear above the first one, and lastly select "Delete".
That's it, you're done. I did this four days ago, and none of the files have rerturned since. Nor have any other files started to grow too large. Hopefully this thread will be helpful to people trying to resolve there internal storage issue.