I used Vonage's Softphone for a while, but found that it it was not as good as SkypeOut. In addition, Skypeout does not charge a monthly fee, whereas a Vonage Softphone is $9.99 in addition to the regular Vonage fees.

Generally Skypeout works well in the hotels as long as the hotel has working high-speed. Same for client sites or random hotspots. Find a nice headset (cost isn't as important as comfort) and you'll like Skypeout a lot more than your cell.