planning to invest upwards of US$100 million in their mobile payments joint venture, people with knowledge of the project have told Bloomberg News.

The Isis joint venture is owned by Verizon Wireless, AT&T and T-Mobile USA.

The mobile networks may invest hundreds of millions of dollars in the venture -- but only if it gains subscribers -- in an attempt to catch up with the mobile wallet platform unveiled by Google earlier this year.

Isis aims to bring mobile commerce...