Does your Modkey have any expansion modules? If not it only supports 2 lines and 8 stations. It can be expanded up to 6 lines depending on the line module and 16 stations. I have not noticed the polarity issue on the ones I have worked on, all modular jacks for lines and stations. It does not support analog phones. The emergency port only supplies dialtone to a analog phone when the system has lost power. I like the NEC DS1000/2000 as an alternative to the Partner ACS. The NEC systems are feature rich and the Intramail voice mail is plug and play. The NEC systems also pass caller ID to single line analog phones including cordless phones. The pricing is very competitive with the Parnter systems. Both systems are very dependable if installed and programmed correctly.