LOL which part of the core issue don't some of you get ?
It is an offence to carry out lewd phone calls on the UK's PSTN, add to this the fact they were left as voice messages and also aired on the radio, all other factors should be irrelevant
Whether it was fun, a prank or for real is largely beside the point, the BBC as the nations main media/news/entertainment company that is funded by joe public has a duty to conduct itself to use the PSTN within its regulations, if they are seen to not give a damn about PSTN misuse then what message would that send out
When such use is breached like this, from within the BBC then they simply cannot condone it and they should be sacked, its really that simple
It's like saying 2 staff from an ISP who send out a virus or spam to a customer for a laugh should be let off because their are worse things to worry about and it was a laugh at the end of the day
All those who constantly claim overreaction, I guarauntee if you were to do this from work tomorrow you would be on a disciplinary at a minimum or even sacked, it is not a trivial offence.