As reported last night, O2 are continuing to have troubles with their network availability for some of their customers. O2 have confirmed the issue is software based and is not localised to a specific geographic area, but affects a percentage of customers across the entirety of their coverage.
Their network status page was updated at 01.00 to read:
We can confirm that the problem with our mobile service is due to a fault with one of our network systems, which has meant some mobile phone numbers are not registering correctly on our network. As a result, some customers are having difficulty making or receiving calls, sending texts or using data. We, and our central supplier, have deployed all possible resources and are working through the night to restore service as soon as possible. We apologise again to customers affected and will provide further updates as soon as we can
And again at 05.40 with:
We’re continuing to drive the recovery of this issue with our support teams and vendors. We’re working to restore service as quickly as possible. Unfortunately we’re unable to confirm any timescales for service restoration at this time. We’ll let you know as soon as we can. We apologise once again for any inconvenience this incident is causing.
As of writing the issue still exists and we’ll update when we know more.