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Step 1: Just put the iPhone 4 Micro SIM into iPad 3G
Step 2: Go to Preferences
Step 3: Go to Cellular Data
Step 4:Change the APN settings as follows:
APN name: wap.cingular
username:
WAP@CINGULARGPRS.COM
password: CINGULAR1
Step 5: You are done, now use Safari and check your internet connection.(It will take some time before the connection picks up)