I'm happy with my N800 using a nokia E65* as a gateway when wifi isn't working. If the N800 had more power available on its USB port I could use my (employer provided) Huawei E172 3G modem adapter. I would guess that wimax adapters in USB form will become available too. Of course, none of this is as elegant as an N810-W but convergence into one device has the downside of converging obsolescence too!

* quad band GSM/GPRS/Edge + 3G (WCDMA - European).