A Tablet has several methods that it can utilize to make a connection into the world:
Both WiFi and Mobile Data Providers connect into the Internet. Any service that uses such a connection may send messages from one device to the other. Email and Instant Messengers like WhatsApp or Telegram can be named here.
Two internet capable devices can also connect through Bluetooth. Bluetooth is a direct connection between two devices, with no router, switch or modem in between. Two devices can communicate through Bluetooth. There are some Bluetooth Messengers out there, even though it does not make much sense (when the two devices are close enough for bluetooth to work, why don't you just communicate directly?). PLUS, there are so-called Bluetooth Hotspots, where you can log onto a hotspot using Bluetooth instead of WiFi.
A Tablet can communicate with a device it is connected to via USB. This option allows 'USB Tethering' for example. In theory, you could also directly connect two phones with USB to enable communication between them.
NFC is short for "Near Field Communication" and does exactly that. NFC sensors are very weak and only work when in very close proximity to another NFC sensor (within another phone). This is a wireless communication with a range of 1 to 10 centimeters.
These are all options a modern phone has to communicate with other devices.