Thanks mpembeivan .
Don't know how accurate this information is
The two countries permit tourists to make day trips from one side to the other without the necessity of obtaining a visa in advance, but visas issued at the border are expensive, particularly upon entering Zimbabwe. In 2008 Zambia increased the prices of their visas, and a U.S. or U.K. citizen can expect to pay US$135 or US$140 for a 3-year multiple-entry visa. Citizens of other nations will pay varying rates for a 3-month Visa, typically about £50, but may need to purchase a visa each time they cross the border.[14] http://en.wikipedia.org/wiki/Victoria_Falls
but I don't want to be stuck in Zimbabwe : let me check if Zambia will issue a multiple entry visa else we'll see the falls only from the Zambian side.