For the safety of the driver and to avoid unpleasant surprises there should be an international standard. Some of them take advantage of the special needs of handicapped drivers. They offer old cars with hand-controls at very high prices, limit rental terms and offer bad service. I was almost trapped with such local company in 1994 in a certain European capital. There are some alternatives for transportation abroad, but none is better than car-rental for independent travel.
Fax is better than phone because of language ''problems'' in many places.
Fast written communication may save a lot of misunderstandings. In some cases even E-mail may work. I found an adapted car in Spain with the help of our embasy in Madrid. In developed countries there are reserved spaces for disabled. Some of them are intended for regional badge holders only.