While my mod doesn't respond to tells asking the time, and does a few things more than what you're after (Banish timers, mainly), it does seem to do most of what you're after.
http://www.wowinterface.com/download...fo.php?id=5640
It will keep track of all the Soulstones cast in the raid (not just your own) and also all the Banishes from the raid (though it doesn't currently remove the timer if the spell doesn't successfully cast--working on it).
The mod will also automatically broadcast to a certain channel (party, raid, channel, etc.) or in tells to a certain person when each soulstone expires. The function can be disabled, so if multiple people use the mod, it won't make too much spam.
If someone asks for the time, you can also click a button to send the current time and Soulstone target to the channel (only the one specified for expired messages though, I'm afraid). It also shows all of the soulstones up at the time, so if you want to send more than one, or a specific timer to chat, you can do so.
When multiple people are using the mod, it also communicates with others when you cast the Soulstone, to ensure accuracy of the soulstone target and time.
(Similar functions are done for the Banish timers, but it doesn't display exact time but shows the time as a bar that changes color as the timer gets closer to expiring. The soulstone timers are just text though.)