Blocked Outgoing Calls?

I'm visiting Uganda from UK I can text but when I try to make a call I am told 'you have blocked outgoing calls'. What should I do?

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Menu Structure (Samsung t239)
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Menu Structure (Samsung t459)
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Menu Structure (Samsung t139)
... Call records All calls Missed calls Incoming calls Outgoing calls Delete all ... IDs Help Service provider info Help text Windows Live Sign in Power on sign ...Windows Live Yahoo! Messages Create message Text message Picture message Inbox Audio ... Friends Work (Unassigned) Speed dial Block list Management View contacts SIM ..., and TIPS for myFaves® (Samsung t139) Text Messaging (Samsung t139) Internet and ...