While there are many reasons that people hide/block their caller ID information, there is no reason for a hospital to do so. In fact, showing up as UNKNOWN to patients and physicians can be quite a hindrance to a hospital's business.
The increasing use of cell phones has made caller ID an expected feature of phone service. As such it has also become commonplace for people to ignore calls from UNKNOWN.
For the last three years I have researched and battled to get our hospital's caller ID information to consistently show up. I say consistently, because some calls would have caller ID and some wouldn't. Finally this year as I was getting into the minute details of our current phone system to write an RFP for a new one it dawned on me what was going on. Only the calls made over our long distance T1 CAS were not showing the caller ID information. After calling several different numbers, I found intelligent life at our long distance provider and was told that it was a simple configuration problem... on THEIR end (be still my heart) that was causing our issue. A week later we had a "cut over" to fix the configuration.
The secret sauce that had been missing for so long is what they call LOCO service. Basically LOCO service tells their switch to send out our number when a call originates from our T1 CAS. Now all is well and the hospital's calls show up correctly for everyone. The moral of the story is that if you're going loco due to caller ID and you have a T1 CAS (not PRI), you need LOCO!