Do you have any information on the call abandon rate between 0800 numbers and 0870/1 numbers? Has there ever been any study on this?
I am not aware of any call abdandon rate studies on this. Your best bet is to ask the telecommunications providers if they've done any studies. Perhaps start with the 870 carrier first and ask them about general abandonment rates. You might probe call set up times as well. As a satellite service provider, it may take longer to set up calls, thus driving high abandonment rates. You also should check with your in-country carrier for the 0800 number to see if they have any statistics on abandonment rates with the various U.S. carriers (assuming you are calling to the U.S.).
Alternatively, if you look at abandon rates for call centers in general (which would generally be using toll-free services), you can get some benchmarks (although these are unlikely to be broken down by number type).