Web callback with one end as Voxalot

[Tranworld]

I tried to set up a web callback where one leg calls via a normal VSP but the other callback leg calls a voxalot number. This did not work and after pressing the CALL button nothing happened, it is ignored? Surely it should be possible? This is because I am using a mobile and wish to talk to someone logged in Voxalot. OK so I can try to callback using one of his provider registered with another VSP, but at this stage (he is trying to set up everything) he is not yet ready and only have Voxalot, what could be simpler to call him via Voxalot, I am surprised that it didn't work !