The calling rules depend on whether he is in a state or federal facility, and the difference is significant.
In most state prisons, inmates in "gen-pop" or general population can make calls as often as they want during the designated phone hours for their unit, as long as there is money in their account to cover the cost. There is no monthly minute cap. If the funds are there, the calls can happen daily or multiple times a day. The limiting factor is account balance, not a built-in restriction on minutes.
In the federal system, the rules are tighter. Federal inmates get 300 minutes per month through the Bureau of Prisons phone system, with that allotment increasing to 400 minutes in November and December for the holidays. Every call costs either six cents per minute for local numbers or twenty-one cents per minute for long distance. InmateAid can get a local number for most federal facilities that brings every call to the six-cent rate, saving $45 a month on 300 minutes for an $8.95 $5.00 monthly line fee.
In the dorms, general population housing in many facilities looks like military barracks. Rows of bunk beds with lockers between them create the only semblance of personal space. Federal dorms typically house around 100 inmates sharing a very limited set of facilities. Six showers, four toilets, four sinks, two urinals, three microwaves, and three sets of washers and dryers for the whole unit. Privacy is essentially nonexistent and learning to exist in close quarters with a large number of people becomes a skill unto itself.
Moving to the general population is a significant step forward from wherever he was before. The phone situation should normalize quickly once he is settled into the unit and has his call list active.