Consolidating your phone lines may mean combining numbers or phones together. Consolidating of course means different things for different people, depending on what you use your phones for. An individual, for instance, may not need a land line if they have a cell phone for both business and personal use. The sophistication of smart phones allow for people to check email, text, and even voice mail on the go. A smart phone may work for a single person, as it combines the advantages of a personal, business, and cell phone needs.
If you have need, there are options for receiving faxes that do not require a dedicated line.
On the other hand, someone with a family may need to keep a land line, if just to allow others to receive and make phone calls. For this, having a business cell phone plus a land line may work out better.
In the end, you want to ensure that you have a manageable number of phone lines. Most phone providers have the ability for call forwarding and number blocking; using these two features can eliminate a phone line, while also making sure that certain people don't have access to a personal number.