Currently Appsync is applicable on the iPhone OS up to 3.1.3 . I think it also works fine with earlier releases of iPhone OS. In case of iPad Apple may approve their installer in order to prevent using cracked apps.

iPad is now jailbreakable! so you can use Appsync for OS 3.2 on it! here is a brief tutorial of what you should done!

1. Jailbreak your iPad using Spirit ( How TO?)
2. Open Cydia
3. Go to Manage Section
4. Select sources
5. Add the following URL into Cydia
   • http://cydia.hackulo.us
6. Click “Add Anyway”
7. Ignore any errors
8. Click on Hackulo source
9. Select “AppSync for OS 3.2
   • iPhone & iPod Touch users should select OS 3.1
10. Click on Install button (upper right corner)  then confirm installation
11. Reboot iPad *IMPORTANT

More detailed info:

• Installing ipa on the iPhone, Step by Step Guide
• How to install cracked ipa on iPad OS 3.2, Appsync 3.2