I wouldn't think area codes would be the issue, but rather long distance vs local call areas which depended on the particular Bell company and/or state regulators. When I was a kid, Seattle and Tacoma were both in the same area code (and are still part of the same LATA) but Seattle was intra-LATA long distance (you had to dial 1 before the number and would be charged per-minute/per-call, but you didn't need the area code) so I couldn't call Seattle BBSes.