One of the things to consider when purchasing VoIP phones to switch your office over to a VoIP hosted PBX system is how many phones you need.
Generally, you will want one phone for the front desk or receptionist and one for each office.
Some companies, however, prefer to have one phone per employee so that if an employee should opt to work from home either on a regular or occasional basis, they can take their phone with them.
When deciding how many VoIP phones to purchase for your small business, be sure to think about how your company uses the phones you have now and whether you need the same number or if getting a different number of phones would make things more efficient.
You certainly want to take cost into consideration, but not at the expense of giving poor customer service by keeping customers on hold too long because that will cost you much, much more in the long run.