Intermittent problems are always the hardest to isolate.
The easiest way check the Sprint system is to swap Line 1 and Line 2 [DIR 748 and DIR 749] and monitor.
If the problem moves positions then the problem is with TELCO, however if the problem stays with DIR 748 then the CO port on the cabinet is bad.
Yes, then you can easily use ports 749 and 750 as Lines 1 & 2.
As a personal preference I would make the old line two the new Line 1 and the 751 the new Line 2.
Also in programming, change the name of DIR 748 to "BADPORT" or something like that...that way the next tech coming down the road in a couple years won't be blind-sided.
As far as I can remember in the Protégé Voice only has a couple things that might need changing.
- Trunk Specific Custom Greetings
I think that's about it. Let me know what you find out.