It's an easy custom function. You just need to remember that a string is really just an array of individual characters, so you can iterate over it. I'll give you an example with text (TX$), a wait amount (WT), and even a sound (BP) as a parameter.
DEF TYPE TX$,WT,BP
FOR I=0 TO LEN(TX$)-1
?TX$[I];
BEEP BP
WAIT WT
NEXT
END
You can then call it like this...
TYPE "SMILEBASIC",10,9
1そうだね プレイ済み