Purchase a Cricket Crosswave, which is a flat device that resembles a smartphone and transmits a mobile broadband connection as a Wi-Fi network to which your Nintendo DSi can connect.
Cricket is an ISP that offers mobile broadband Internet, which is Internet that is delivered via cellphone towers via a USB or PCMCIA card. Though these cards are often used with laptop and desktop computers, it can also be used with handheld Internet-enabled devices, such as Nintendo's DSi, with the aid of a mobile broadband Wi-Fi router.
Sign up for a Cricket mobile broadband account if you don't already have one; otherwise register the device with your existing subscription via your Cricket account. Provide up-to-date billing information and any required personal information, such as your name, address and phone number.
Place the Cricket Crosswave on a flat surface in the room where you plan to use your Nintendo DSi. Turn the device on by pressing the "Power" button. It will begin transmitting mobile broadband.
Turn on your Nintendo DSi, and select the "Wrench" icon. Select "Internet," then "Connection Settings." Tap the drop-down menu next to "Connection 1," and select "Search for an Access Point." The Nintendo DSi will search for an available wireless connection and will display your Cricket Crosswave's Wi-Fi hotspot signal when it finds it. Select the wireless network; then tap "Connect."