It truly is 1996 allover again; only this time it's the mobile web instead of the world wide web. Case in point, every other week there seems to be another new search engine (only now it's for mobile searches).
The one you may have not heard of, however, is Taptu.
Of the four, I found that Taptu loads the fastest (a big plus). For iPhone users, keep an eye out for Taptu's new iPhone app launching soon. It's optimized for the touch screen apparantly.
That being said, I like Bing so far. It is the easiest to set for local searches and didn't require a registration. I only had to submit my zip code. Yahoo! and Google, well, were Yahoo! and Google.
The jury is still out on all four. I'll keep you posted as I play some more.