Still one more class-action lawsuit is claiming that the iPhone not only fails to live up to 3G speeds, but that it also prematurely develops hairline cracks in its outer casing, and that AT&T has oversold its 3G bandwidth with the iPhone.

Texas residents Alyce R. Payne, William French, Karen Michaels, and Lorna Harris filed the long and bulky 23-page complaint in an Eastern Texas court on their own behalf as well as all customers who are not satisfied with their iPhone 3G purchase, claiming that Apple has committed breaches of contract and warranty, violating Texas business and commerce codes, and many other infractions.

The suit is the second to be filed this week (among many others over the past several months) claiming the iPhone 3G performs poorly when connected via 3G because it “demand(s) too much power from the 3G bandwidths” and that both Apple and AT&T are aware that the performance is nowhere near what it promises its customers in their ads and representation.

It’ll be interesting to see how this turns out. Odds are it’ll be settled with money, but hopefully both vendors will take it as a sign that however marvelous the iPhone is, it still has room for improvement.