In general, you can call the medical facility where the patient is being treated and ask for a specific patient's phone number. Federal privacy laws allow hospitals to give out directory information - room or phone numbers - for a particular patient unless the patient opts to have their name removed from the distribution list.
Depending on its amenities, a medical facility might employ staff at an information desk or maintain an automated phone system to answer questions concerning patient directory information. Many medical facilities offer a dedicated phone line for directory assistance.
The Health Insurance Portability Accountability Act, enacted in 1996, regulates what medical information can be released and to whom. Medical staff are not allowed to release information that would compromise the confidentiality of a patient's medical care. According to federal privacy laws, those requesting a phone number must invoke the name of the patient; they are not allowed to peruse a list of patients currently treated at the hospital.
In many cases, the number of a patient's direct phone line incorporates their room number. Some hospitals offer the option to contact a patient in other ways through their website, including email, e-greetings or other forms of electronic communication.