If you can't get a good prepaid phone card or your home long distance carrier calling card doesn't work, you may want to look into renting a cellular phone that works from the city in Kenya you will be visiting.

I was in South Africa and I rented a cellular phone. It was about $7/day + .99 day optional insurance (highly recommended) and about $2.70 per minute phone charge. You can rent for as little as one week. Delivery and return is by fed ex delivery to your home. You have two days from your return date to send back the phone without incurring another day's charge.

There are a number of cellular phone rental companies. I searched on the internet and found a good number of rental firms to choose from.

I am not sure about Kenya, but considering what hotel long distance rates are from western Europe, I would have to imagine that $2.70 has got to be cheaper than hotel phone charges from Kenya.