Fixed line vs Cellular
Cell phones have limited coverage area, unless in a big city with a lot cell phone towers, but there are other ways the signals can be blocked as well. Which makes a cell phone less dependable. The batteries in a cell phone need to stay charged to make or receive calls, and as long as it is charged you can use your phone any time even if you are somewhere where there is no power. Cell phone plans are usually cheaper is you are just getting a plan to talk on the phone and not a plan that includes data. A land line always works (unless it a cordless phone and the power goes out). You do not need to charge a land line phone that is connected to the wall, and you do not have to worry about a weak signal. The cost is more especially if you need to make long distance calls because that is not included in a normal plan.

Voice vs Data
Cell phones use both, you can use the voice and data at the same time because they no longer use the same antenna.
Landlines phones use both, the key tones use data because the tones transfer as data, and you talking is using the voice
SMS/text uses data, and is transferred as a message with characters over the data network
Fax uses the data, when a fax is sent it gets immediately digitized and packaged in secure TCP packets and sent to natural data inc and then secure networks operation center for final delivery.
Pagers use data, they receive a number via a small screen from incoming callers
VOIP uses the data network over the internet and bypasses the phone companies making all calls via the internet.

Online Gaming
When it comes to gaming, you start with your internet at home, contact a series of switches that are governed by the traffic management interfaces, and then the user will access the game servers and databases. This all allows multiple users to connect to the servers and with each other