Vodafone continues to sweeten its mobile broadband deals ahead of Telecom’s “T Day” launch of its own 3G network in June.

While mobile data remains bracingly more expensive than landline broadband, a flurry of new plans are helping to narrow the gap. Expect more, and sharper deals - including tastier 12 and 24-month contracts - as T Day bears down.

Vodafone’s new Broadband Surfer deal, available only to Supa Prepay customers, gives you $40 a month for 512MB of data.

The carrier’s welcome move away from nosebleed excess data charges continues with the new plan.

If you exceed 512MB of data, you can buy another block of 512MB for $40.

But you can also mix-and-match casual plans, choosing to trip onto Vodafone’s $1/10MB a day deal when your 512MB runs out, or its other recently-announced plan, which offers 100MB/month for $10.

Alternatively, you can head in the other direction and buy a $40 block of 512MB if you think you’re in for a heavy month.

Vodafone’s GM of Products and Pricing Paul Toomey says anyone can use their mobiles as a modem with this plan, or simply buy a new SIM dedicated to data:

“If you’ve got a Vodem Stick or a Vodafone Connect Card but don’t need ongoing monthly data, then Broadband Surfer lets you use what you need, when you need it. We’ll let you know when you’re at 90% usage and again at 100% with a txt.”

Existing Supa Prepay users can add Broadband Surfer to their phones by sending 'BUYTopUp512MB" to 756. New customers will need to go in store to buy a new SIM and have it activated for prepay data.

Broadband Surfer comes on the heels of Vodafone’s $10/100MB a month plan, and a zero-dollars-up-front deal to get a Dell Inspiron 9 netbook on a two-year data contract.

Telecom is so far staying mum on its T Day deals, but did recently introduce a recession-fighting “success pack”, which lets a business break its mobile contract, among other perks, if it can prove it’s struggling.