1, 3 and 7 normally - although some PBXs do need different pin conditions. Don't wire Pin 2 as you don't want to be sending anything back to the PBX.
For very high quality cabling and up to a maximum of 9600 baud yep 150ft is your limit, on bog standard cabling you're looking more like 50ft. That's a lot of serial cable though! You could use line drivers to boost the signal but to be honest they're flaky. Consider Serial->IP convertors or putting it over modem.