Vodafone launched a flat rate data tariff on Wednesday, making it cheaper for users to surf outside of the operator’s walled garden.

Vodafone Mobile Internet is available to most customers, and a platform that re-renders typical internet web pages for display on the mobile has been tested on 150 different handsets.

The fruits of Big Red’s recent partnerships with eBay, Google, MySpace, Yahoo! and YouTube are also evident, with features such as Google search prominently displayed.

Contract customers signing up to a data pack will pay £7.50 for 120MB of data per month, and will be charged in the same way as customers who have not signed up for the pack if they go over this limit.

A customer not signing up to a data pack will pay £1 for 500KB of usage each day, but will not experience further costs until they have used 15MB. Usage of less than 500KB will incur a proportionately lower charge.

Prepay customers will be charged in the same way as those who have not signed up to a monthly data pack.

Vodafone is keen to specify that the data packages are for mobile internet usage only. This means services such as VoIP or “peer to peer services such as instant messenger services, text messaging clients or file sharing,” will not count towards the £1 per day charge or monthly bundle and are charged separately at £2 per MB, with a £0.05 minimum charge for each data session.

In the past Vodafone has muttered something about the fact that it is still “testing VoIP,” which is why it is so reluctant to facilitate the use of the technology – the company recently launched a crippled version of the Nokia N95, which had the VoIP functionality removed.

But we think it is more likely to be something to do with Vodafone’s ‘Starfish’ project.

At the CeBit tech conference in Hanover in March, Vodafone demonstrated Starfish, the launch application for a combination of IP services including MSN Messenger, Skype and AOL IM.

Rival UK operator Orange also launched its own flat rate mobile internet offering for both prepay and contract subscribers this week.

For Orange users, daily browsing for all subscribers is charged at £1, with prepay users able to sign up for a seven day browsing package for £5. Monthly contract subscribers can also sign up for a monthly evening and weekend browsing package for £5, or a monthly anytime package for £8.

However, Orange has come under heavy fire for capping its usage at 30MB.

Bu Voda’s reckoning 120MB could give a user up to 4 hours watching YouTube or viewing of up to 160 mobile internet pages every day for a month or the ability to check and reply to urgent emails 10 times a day for a month.

Presumably this means Orange users get a quarter of that kind of usage for £0.50 more per month.