In Japan I often have to call somewhere and explain my name such that the person on the other end can write it down. My name is "Sepponen Bemmu", which I want them to write down as "セッポネン・ベンム".
Is there a way to "spell" katakana verbally?
Generally you just read out the individual kana, and for little-tsu you can say
If there is some confusion you can say the "group" of kana it's in, then say
For separating your first and last names I'm not sure if the person you're speaking with will realize they're separate, so you would add in
So, if you wanted to spell your name it would be something along the lines of this:
At least, that is how I would do it.
I realize it's a bit difficult to understand without hearing it, but hopefully I explained myself clearly...