Japan's NTT will expand its partnership with PLDT, and may pay $263 million to maintain its 20% stake in the Philippine operator.
NTT subsidiary DoCoMo has flagged plans to establish a joint business co-operation committee with PLDT as well as its mobile subsidiary Smart.
DoCoMo has also entered an option agreement to acquire around 2% of PLDT's share capital from investor JG Summit.
The option will be taken if PLDT manages to close the acquisition of a controlling stake in rival Digitel in a transaction that could involve a share-swap component.
The PLDT-Digitel deal has been arranged, but there is a question as to whether regulators will approve a merger that could at least temporarily return the Philippines' telecom market to a duopoly.
DoCoMo said the option agreement is aimed at protecting the NTT group's combined 20% holding – including the 7% stake held by DoCoMo itself – from dilution.
DoCoMo first acquired its 7% holding in March 2006, and the NTT group's holding hit 20% in February 2008.
The operator separately announced an agreement with Twitter to develop mobile apps and services incorporating features of the social network site.
DoCoMo said it will first incorporate real-time tweets and other content into the search results on its i-mode portal (for feature phones) and DoCoMo market (for smartphones) either late this year or early into the next.