@Wexfordman,
Hullomail's actually a hosted voicemail system operated by a private company separate from your mobile operator. It is not a digital answering machine in your phone.
The software you install on your phone sets up conditional diverts to an 076 VoIP number that is used to access your voicemail box on their system.
So, when a call comes to your phone, instead of being diverted to your network voicemail it goes to Hullomail's 076 number.
The messages are then made available to you through the app on your phone and can be played directly without any need to dial into anything (data connection is required to download them) i.e. visual voicemail.
Or, you can dial into their system and use a pin like old fashioned traditional voicemail.
It also delivers the message to your email account if you set that up.
It also has some fancy functions like it can play out specific messages to specific numbers. Or, it even run the messages through voice recognition software and produce a rough transcript of what's said so you don't have to go to the hassle of listening to everything.
When someone calls from a 'blocked number', all that happens is the number is your local exchange / mobile network sends the call to the receiving exchange/switch with a flag attached that indicates the number should not be displayed. Your number is still sent, and the receiving exchange knows it and may log it in its records. The system trusts the exchange at the end of the route to respect that flag and not display the number.
There was apparently brief glitch on the HulloMail servers that meant those flags were being ignored and blocked numbers were displaying. So, when the app displayed a voicemail or a missed call, it was getting the full blocked number from the server.
They've fixed that issue now and blocked numbers no longer appear as anything other than "Private Number"
Basically, if you call from any phone, your number is always sent and can be retrieved by the receiving party's phone system. Some office systems don't necessarily respect that flag either and when your call is going outside Ireland and onto VoIP networks you've no idea what level of access the end user might have or whether the system is programmed to understand those display / do not display flags. So, I would absolutely never assume that your calling line identity is absolutely private.
In cases of harassment or criminal activity, the police services can most certainly also request access to the logs from the local exchange at the receiving end and it will have all that data stored in its log files. So, it can be quite easily retrieved.
Basically, if you're dumb enough to make harassing phone calls, you can be caught out very easily!