I have a request for the phone booth in the Dr Who series. Can anyone give me ideas on how to achieve this cake and how large would it need to be to feed 15? I'm worried about stability and the cake making it to it's destination still standing.

I forgot to ask what frosting should I use? I am worried that fondant would be to heaving for this cake.

4" square 8" tall is 16 servings -- this would basically be a two tier cake -- so you need to dowel the bottom tier and since this is so small -- i would use 4 skinny straws to dowel the bottom tier then place the board and mark where the straws are located and insert long bamboo skewers into the straws to help hold up the top tier so it doesn't fall over and push then all the way down into a layer of foam under the bottom board for stability -- deliver cold --

you could use any kind of buttercream -- another idea would be to use candy clay for a covering -- you could just cut panels and apply to the buttercream -- you could do that with dried fondant/gum paste panels too 

http://www.cakecentral.com/recipe/query/candy-clay