While T-Mobile isn’t bashing AT&T in advertising as badly as it did before the announced proposition of a merger between the two companies, T-Mobile is still calling out AT&T’s high mobile prices with innovative new service plans that can deliver substantial savings for consumers — savings that will evaporate if AT&T swallows the company whole.

Take this week’s introduction of T-Mobile’s new Family Mobile Unlimited Plans, which deliver unlimited texting, calling, and 2GB of throttle-free “4G” (HSPA+/HSPA+42) data for as low as $69.99 per line (two-line minimum), which is just shy of $140 a month before taxes and fees.  Comparable plans from AT&T run $99.99 per line — a $30 difference.  A two year contract is required.

Although T-Mobile is pitching these plans as delivering “unlimited data,” in reality their speed throttle kicks in on some of them after 2GB of usage per month.  While customers will not experience bill shock from overlimit fees common with AT&T and Verizon Wireless, they won’t actually get an unlimited data experience like the one Sprint still delivers on its unlimited data plans.

Additional lines are available for $20 a month with 500 calling minutes and 200MB of data usage, or $40 a month each to upgrade to unlimited talk (but keep the same 200MB usage allowance for data.)

T-Mobile is pitching these plans to value-conscious families who live on their phones.  While other providers let you pool calling minutes on Family Plans, each phone usually has to also select any additional added-cost features like data and texting.  T-Mobile is bundling some of these features into the sale price.

AT&T told investors the merger would bring about higher revenue and cost savings.  Not having to respond to T-Mobile’s aggressive price competition by lowering its own prices is one great way to achieve this.

That means higher prices for everyone.