When someone is arrested and taken to jail, at some point, they are provided access to a phone; if the defendant can't remember any phone numbers, they may be out of luck.
Jailers always take an inmates personal possessions as part of the county jail booking process. This can include everything from confiscating watches, purses, jewelry, car keys and yes, this includes the defendant's cell phone. These items will be returned to an inmate when they are released but they won't have access to any of it while they remain in custody.
Although it is common practice for the jail to allow an inmate to make outgoing calls to loved ones jailers won't give someone back their cell phone if they can't remember any phone numbers.
Being arrested and taken to jail is traumatic all on its own, but not being able to contact a friend or family member so they can help arrange for bail bonds can have an already bad situation seem that much worse. As a rule of thumb it is always a good idea to commit several phone numbers to memory, just in case.
This could include those of your parents, siblings, significant other or even a roommate. The more contact information you are able to call, the better, especially if you find yourself being placed in handcuffs, taken to jail and charged with a felony crime.