We did check rates on some cheap phone cards and found they were slightly higher than REBTEL's normal rates when one includes all service fees and taxes. Check here for some phone card options.
We also check rates using the Tel3Advantage Savings Plan and found that their normal rates were about the same. Using the Savings Plan the rates are 9.2 cents per minute on calls to land-lines and 31.9 cents per minute on calls to mobile phones. However, Tel3Advantage also has a special offer for new customers. If a new customers opens and account and deposits $10 they will also deposit $10 so the customer can make $20 worth of calls for only $10. Visit the link above for the Tel3Advantage Savings plan or call 1 800 441 0321 for more details.
It looks like REBTEL and Tel3Advantage both offer pretty good rates on international calls to Zimbabwe. Those interested should likely try both services in order to find the one they like the most while taking advantage of low introductory rates.