Android users regularly lord the “openness” of their phone’s operating system over iPhone users, but the truth is far more complicated. The latest example of that came this week when Android phone users found themselves unable to download “tethering” apps from the Android Market.

[ad#Google Adsense 300×250 in story]Tethering apps enable Android-equipped phones to act as a Wi-Fi hotspot for other devices to use to connect to the Internet. They’re handy for users on the go who want to share their phone’s data connection with other devices – a laptop, a tablet, and so on.

The capability exists in both AT&T and Verizon iPhone 4 models as “Personal Hotspot,” and is activated when the iPhone user subscribes to a carrier data plan with that capability – typically a $15 to $20 a month premium on top of basic data plans.

Tethering applications run afoul of those carrier restrictions, and the Android Market now prevents those applications from being downloaded by customers using carriers including AT&T, T-Mobile and Verizon.

Sprint is the notable holdout. Sprint advertises its “Simply Everything” plans as unlimited – the company runs TV ads featuring CEO Dan Hesse lauding the plans as “truly unlimited.”