Usefulness of Mobile call back?

[Tranworld]

Technically this is a great feature but I struggled to find a practical situation where I would want to use this.

Imagine this scenario where I am at a public hotspot, take out my E61, log in and initiate a call back, the phone ring, I got connected and talk...sounds right but then, if I have net access already I might as well use the SIP function on my E61 (which register very well with Voxalot, thank you) and make that call using just one leg of the VSP.
Or if I am at home with ready Internet access, I can't think of why I would use a call back.

Of course not all Internet phone has SIP client, granted, but pretty soon they will, I would hazard a guess.

So frankly once you have Internet access, there is little reason to use call back.

What would really be useful is if there is a way to initiate that call back using a normal call back technique of a a PSTN number that you call, it drop the line and then call you back (using the web callback technique of course), except in this case you can chose your VSP and the rate etc. now that will be really really useful.