[Coda]

「3DSにかなを書けない」
"3DS ni kana wo kakenai"
literally "Kana cannot be written on a 3DS" but context usually implies "I cannot write kana on a 3DS".

You might also choose to say "kana de" instead of "kana wo" -- the difference is "writing with kana" instead of "writing kana". There's not a substantial difference in meaning, although I suppose "de" might be slightly preferable because obviously you can draw a picture of a kana in a picture message.