The phrase "about which service" is correct and usable in written English.
It can be used when referring to a specific service in a context where clarification or additional information is needed.
Example: "I have some questions about which service would be best for our needs."
Alternatives: "regarding which service" or "concerning which service".
Clearly, making a choice about which service to use to reduce the cost of international calling will depend heavily on what cellphone you have and whether you have easy access to a Wi-Fi network.
A new pricing scheme is forcing Netflix's 25 million customers to think about which service they want — access to online streams, access to DVDs by mail or both — and some have decided to rethink the monthly splurge entirely.
This is because delivering public services is different from working in other markets – they are funded by taxpayers and often people cannot have a choice about which service they use.
You don't have to think about which service to use — moreover, driving a Tesla is cool.
There is a lack of evidence to support decisions about which service to provide for overweight children.
There also needs to be clarity about which service will take responsibility for ensuring the family have access to bereavement services.
Town halls will now face extremely tough choices about which services they can keep on running.
That means tough decisions must be made about which services are provided, to whom and at what expense.
Health-care costs ultimately arise from the accumulation of individual decisions doctors make about which services and treatments to write an order for.
Disputes about which services need to be on the same site need to be resolved in advance or compelling evidence published to counter anyone who breaks ranks.
The next few years will be a challenge for local councils, which face a £5.8bn funding gap by 2020, according to LGA figures, and difficult decisions about which services are scaled back or stopped.
