Yahoo and T-Mobile have announced a partnership deal that will have Yahoo search powering T-Mobile’s newly created web2go portal. This means that when a user goes to use their T-mobile web2go portal, Yahoo will be the default search engine built-in.

Also, Yahoo advertising will be featured on search-result pages, with both T-Mobile and Yahoo will sharing the revenue from those ads.

How big is this? Well, T-Mobile boasts over thirty-two million US subscribers, and with mobile web capabilities increasing, more and more of them are signing up for data plans — a big money maker for T-Mobile.

How necessary is this deal for Yahoo? As of September, an estimated sixty percent of mobile internet users tended to use Google search, with Yahoo claiming thirty-six percent of the market share. Yahoo needs to improve these numbers in order to ward off long-term mobile dominance from Google.