All four of the major wireless carriers in the US are preparing for Apple’s big announcement tomorrow, although one company’s plans will be vastly different than the rest. T-Mobile, the lone carrier that still hasn’t worked out a deal with Apple to carry the popular handset, is preparing to launch a campaign inviting users to bring their own unlocked iPhone to the network.

The idea is that because T-Mobile won’t have to subsidize the cost of the handset, they can offer service plans at a cheaper rate than their competitors. The wireless carrier is planning to have an unlocked iPhone available in every retail store to validate the “unlocked and unlimited” marketing campaign.

The nation’s fourth largest wireless carrier says plans will start around $60 for heavy data users which could save roughly $50 per month over comparable AT&T plans. The company already has nearly a million iPhones on their network.

Saving money is a high priority for many people in this economy but T-Mobile’s offering does come with one major flaw – their network doesn’t yet fully support the spectrum needed for the iPhone. This means that almost all customers will be restricted to running on a much slower 2G network. The carrier is in the process of upgrading their network but for now, it’s still going to be slow for most everyone. Furthermore, only iPhones designed to run on AT&T’s network need apply as it uses the same GSM standard that T-Mobile uses.

The marketing effort is expected to go into full swing tomorrow as Apple announces the next generation iPhone at a media event in California.