The news comes just days after iPhone carrier AT&T said it had chosen Yahoo as the default search engine for the Android-based Motorola Backflip, eWeek reports.
While T-Mobile USA has replaced Yahoo with Google as its default search engine on mobile phones such as RIM BlackBerrys, some Yahoo-based services will continue to work on T-Mobile, including Yahoo Mail and Yahoo messenger.
A Yahoo spokesperson stressed that T-Mobile and Yahoo would continue to work together on content services such as Yahoo News, Yahoo Sports, Yahoo Finance, Flickr and weather on T-Mobile’s Web2Go portal.
However, the portal itself – which provides search services to non-smartphone internet users – will now be powered by Google.
Despite this, some website optimisation experts have claimed that default search portals will mean increasingly less as smartphones become more popular.
Greg Sterling of Search Engine Land said that "this switcheroo of the T-Mobile ‘default’ relationship doesn’t necessarily help Google or harm Yahoo in a major way".
"Consumers have more options to access the content and services they are loyal to on smartphones, rather than simply accepting and using the carrier-designated services," he added.
However, he continued that there would no doubt be some incremental loss or gain in terms of search query volume and related clicks.
The alliances between search engines and mobile carriers have become an important part of the website optimisation (SEO) landscape, according to SEO practitioners.
For example, research published earlier this year by the Internet Advertising Bureau revealed organisations that combined mobile and website marketing were able to radically increase brand awareness with a 150 per cent higher click-through rate online.