AFTER 17 MONTHS of using my Huawei 585 on two continents, I can wholeheartedly endorse the use of portable wifi service.
Using a device like the Huawei 585 (at left) or the O2 Hotshot eliminates the need to tether from your mobile phone and that means you won't face any sort of bill shock after tethering for 10 minutes. I bought the little black Hauwei 585 from eBay for EUR 60 but if I'd renewed my data contract with O2 I could have received it for free.
I can feed my over the air data habit with a Pay As You Go SIM for less than 20 EUR a month. That's the price point of the contract I'd have to maintain with O2-Ireland for the same peace of mind. Both the PAYG and the standard contract for O2 data worked elegantly in Ireland, England and the States for me. I've powered creative multimedia classrooms with this Hauwei hotspot, lit up entire carriages on Irish Rail with it and its the high speed connection for the iPad while we're underway in Ireland.
If you haven't worked out a plan to tether before you need to tether, you might be in for a surprise about the cost of running your phone in tethering mode.
Some of Bernie Goldbach's curated mobile links:
John Rutledge -- Lessons from a Road Warrior: How I fell off a horse, earned 15 million air miles, got sand in my shoes and learned how to invest. Get it on Kindle.
Speeding Along with O2-Ireland's Dongle (insideview.ie)