Three or Giffgaff for the IPhone! Three offer unlimited all you can eat data with tethering. Giffgaff only offer unlimited data for browsing NO Unlimited tethering. Tethering means sharing the Internet connection of an Internet-capable mobile phone with other devices. This sharing can be offered over a wireless LAN (Wi-Fi), or over Bluetooth, or by physical connection using a cable. In the case of tethering over wireless LAN, the feature may be branded as a mobile hotspot. The Internet-connected mobile phone acts as a portable router when providing tethering services to others.