As backpick25 suggested, it wouldn't be a bad idea (or practice) for your son to ask the coaches how often they'd like to talk the next time he speaks to them. I think it is most important to understand why they offered with no deadline. There has to be a logical reason.
My son's experience was similar to ffxfireman where my son was offered by the AC with no deadline. 3-4 weeks later (after the initial offer) there was an absolute deadline (72 hours - over the weekend) as my son was headed off to a prospect camp at another school. My son's travel coach leaked some information about the prospect campe, and they came back to us with a larger scholarship offer but a firm deadline. After the initial offer, my son tried to communicate with the AC and RC on a regular basis but frankly they were difficult to get in touch with as they were travelling constantly. This was his dream school when he was growing up, so it was an offer he took very seriously.
So, we found out years ago (through several members of HSBBWeb) that initially offering 25% with no deadline was standard operating procedure with this specific D1 school. Their admission standards are high, and it is a fairly expensive D1 in the south. This is their way of finding out how interested a recruit is in their school while they continue to shop around for additional recruits. Essentially, my son was the first local recruit to meet their needs (after seeing him play 6+ times + a couple unofficial visits) so they decided to offer. It was his first offer, and frankly it was a God send at the time. So, I would do my due diligence with the Financial Aid office, look into any academic scholarships that may be available, and continue to compare the school to other opportunities. I can guarantee you the school will continue to look at other talent. In my son's case they found someone in CT that was similar to him, and then they put the 72 hour full court press on him. So, while the offer is great in some regards I wouldn't be too surprised to get a phone call asking your son to decide with a specific date and time. At least that was our experience.
Good luck!