Most people don’t know much about phone systems short of the fact that as long as it is up and running, that is all that matters. If you’re just starting out or what want to switch phone systems, you should know your options. Here is a breakdown of the different telephone systems according to size of company.
10 Employees or less: KSU-Less System: This is the best option for small companies who are not trying to grow and do not need multiple extensions or phone lines. This is not advisable for startup companies whose needs may change greatly in a matter of a few years. 
         
          Perks/Features: Inexpensive, portable (can be taken with you if you move),  voicemail, up to 4 lines and 8 telephones, extensions, telecom, no cabinet.
          Downside: Not compatible with PBX phone systems, might have to hire out maintenance and installation as most vendors don’t provide these services with KSU-less systems. If need more extensions than what it comes with, you will need a whole new phone system.

10 to 40 Employees: Key Systems: This is ideal for a medium sized company who needs many lines and extensions. 
         
          Perks/Features: Relatively inexpensive, easy upgrades, customizable features, hybrid option: combines PBX with Key systems giving the features of PBX at a lower price

          Downside: Requires a cabinet (may take too much space for some smaller companies), not as customizable as PBX

40+ Employeses: PBX Systems: This phone system allows for the most growth because of the ability to easily add extensions. For companies that expect much growth, this option is better than the Key system.

          Perk/Feature: Easiest system to upgrade and customize, more features than most phones, 

          Downside: Most Expensive

Any size: VoIP Systems(Voice Over Internet Protocol): Rather than using a phone line, this uses an existing fast internet connection to make calls. T1 lines are the best for VoIP systems.

          Perk/Feature: Inexpensive, customizable, lots of additional features, long distance (including international calls) are not expensive

          Downside/Necessary Office Upgrades for VoIP:
          • Equipment: Need VoIP specific phones or adaptors
          • Internet Connection: Upgrade internet connection speed and bandwidth to handle increase in data transfer
          • Power outages: (Cut the phone service) installing backup power generators or having an emergency landline alleviates this problem
          • 911 calls: VoIP doesn’t have geographic tracking—you need to install E911 or a backup landline for emergencies
          • Security: Calls can be hacked via internet and you must install security measures to prevent this

Telephone systems are a vital part of most office communications. Not only are they important for internal communcations but externally as well. Breaking down the phone systems options by size may help you determine what phone system is great for where you are now, but keep in mind what the size of your company may be in the future. Understanding what fluctuations in company size means for your phone system is important as the phone system you select will (hopefully) be with your company for a long time. Replacing phone systems is a long and expensive process, this guide will help you get it right the fist time.

Monique L. Myers is a writer, surf instructor and an art enthusiast based in San Diego, California. She writes extensively for Resource Nation, an online resource that provides expert advice on purchasing and outsourcing decisions for small business owners and entrepreneurs.

Resource Nation provides free tools, tips, and purchasing advice for business owners and entrepreneurs in over 100 business categories ranging from phone systems to credit card processing. Whether it's connecting businesses with local and national pre-screened vendors, or offering easy service comparisons on a VoIP service, Resource Nation empowers business decision makers by providing the information they need to make smart choices.