One option is to use your phone's built-in tethering ability, which means you'll likely have to pay your carrier an extra fee for the service. The other is to download a third-party tethering app such as PdaNet (for nonrooted Android phones), Wireless Tether for Root Users (for rooted Android phones), or PdaNet for iPhone (for jailbroken phones).
The only problem with tethering is that carriers do their utmost to discourage it. If you use your phone's default tethering ability, you'll have to pay your carrier a fee of around $20 for the privilege. That's $20 on top of your already pricey data plan--and you don't get any extra data.
And if you use a third-party tethering app, your carrier can charge you if it finds out (unless you happen to be on Verizon). And only jailbroken iPhones can run third-party tethering apps.
But jailbreaking, rooting, or paying a monthly fee may be a small price to pay for the freedom to use your Wi-Fi only tablet (and other devices, such as your laptop) wherever you can use your phone.
2. Get a Mobile Hotspot
Instead of tethering your tablet to your phone's data plan, you may want to consider picking up a mobile hotspot from your local wireless carrier.
A dedicated mobile hotspot can yield better results than tethering your phone's data connection. For starters, it's often faster and more reliable than a tethered phone's connection. And whereas tethering can drain a phone's battery quickly, mobile hotspots commonly deliver many hours of battery life.
I use the Novatel Wireless MiFi 4510L for Verizon LTE, which offers long battery life, excellent data speeds, and a solid connection--unlike my Galaxy Nexus phone.
Though the MiFi 4510L lost out in PCWorld's hotspot tests to the Samsung 4G LTE Mobile Hotspot, the main advantage of the MiFi 4510L is its ability to keep its connection while moving. The Samsung 4G LTE is speedier when you're sitting still, but, in my hands-on experience, the MiFi 4510L maintained a solid connection on a 9-hour drive to Vegas (our PCWorld tests didn't evaluate this capability).