3 and Skype have announced the launch of a 3G handset with Skype built in.
Pre-pay customers will need to spend at least £10 per month, so you can see how 3 may be justifying the move - loose out on potential call revenue beyond any inclusive minutes, but retain and attract plenty of customers. The only other risk would be overstretching their bandwidth, but they seem to have plenty of unused capacity.
Interestingly, the phone was developed with Qualcomm and is therefore Brew-based. It does however seem to also support Java.