There are charges for using USSD service. These charges will vary country-to-country, or these charges can even vary between mobile network providers, and subscriber plans (i.e., pre-paid versus post-paid). In Kenya, for example, a pre-paid subscriber will pay KSh 1 (about $0.01) per USSD command on Safaricom, the largest mobile network provider in the country.
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I can't believe the MNOs charge for USSD. What a ripoff. Boo
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