Ooh, that's a lateral solution. I don't know; my own mobile doesn't even have a compose function as far as I know :-/

I don't think there's a standard there, but ICBW.

Some phones support MIDI files; others use some bastardisation thereof.

I guess most people download ringtones etc these days, rather than entering them manually. My phone certainly has a function where I can type in something like d1b1d1b1g2, and have it play oranges and lemons at me. I forget how it handles octaves, but it does manage a couple.

Aha! Now I remember: Ring-Tone Text Transfer Language (BNF), and an RTTTL to MIDI converter (untested)

Ah, and you can write a player for it with the system beep:

($B,$D,$O,$/)=(63,4,6);$f{(qw/C C# D D# E F F# G G# A A# H/)[$_%12].(int($_/12)
+2)}=440*(2**(1/12))**($_-45)for(1..88);for(split(/[^\w\=\#\.]+/, uc(<>))){if(
/(\w)=(\d+)/){$$1=$2;next}if(/^(\d*)([PA-H]\#?)(\.?)(\d?)$/){$n=($3?60:90)/$B/
($1||$D);`@{["xset b 75 ".int($f{$2.($4||$O)}||1)." ".($2=~/P/?0:int($n*1000))]
}`;print chr(7),`sleep $n`}} # I apologise for this, I really do. I was bored.