If you're rooted but on stock rom, do this to stop OTA's:
The actual OTA download will be located in /cache. Delete with Root Browser or Root File Manager if present.
Freeze via Titanium Backup: FWUpgrade.apk and SDM.apk
Use Root Browser or Root File Manager to:
Rename file: /etc/security/otacerts.zip to otacerts.zip.bak
Rename file: /system/app/ wssyncmlnps.apk to wssyncmlnps.apk.bak
Then do the following:
1. Open Root Browser or Root File Manager
2. Navigate to data/fota
3. Long Press and select Permissions
4. Uncheck all boxes making it 0000
The last bit is overkill, but you can do it if the OCD kicks in.
Just Say No to root-killing updates