Goldman Sachs has reviewed the implications of Frontier Communications assuming control of millions of Verizon landline customers, and promptly downgraded their stock to a Neutral rating, telling investors the upcoming consolidation will hasten eroding revenues at Frontier.

“Consolidation of the underperforming acquired assets causes an immediate step-up in revenue erosion for FTR (-6.3% in 2010). In addition, the combined company’s initial EBITDA margins will be significantly below those of legacy FTR (pro forma of 48.0% in 2010, 470 bp below legacy FTR).”

Analysts added, “We expect longer term EBITDA margins of 50%-plus, driven by synergy realization (we forecast $450 mn/year by 2013), and moderating revenue declines, as FTR is able to bring a more localized focus to assets that were not a primary focus inside of a much larger Verizon entity. We forecast 2011/2012 FCF of $950 mn/$921 mn, as synergies and margin expansion only partially offset continued (but moderating) revenue erosion.”

In English, that means Frontier will benefit from its larger customer base in reducing expenses on a per-customer basis, and could become a big enough player to realize some benefits from rolling out services to a larger number of customers nationwide, but those benefits will be tempered by the ongoing loss of revenue as customers dump Frontier landlines for wireless and, where available, switch to a cable modem product to get better speeds and consistent service that Frontier DSL does not provide.  Losing that 5 GB monthly usage allowance won’t hurt either.

Frontier is betting a good deal of the company on expanding broadband service in its largely rural service areas, where many Americans are still stuck relying on dial-up or satellite fraudband, the service that promises a broadband experience but doesn’t come close to actually delivering one.

As long as Frontier doesn’t face competition in its markets, it can deliver 1-3 Mbps DSL service for up to $50 a month and bank those profits as a firewall against ongoing loss of landline revenue.  But if new players arrive, such as LTE wireless, WiMax, cable, or municipal fiber, Frontier’s business plan could go awry in a hurry.

Frontier also continues to pin its hopes on its enormous payout of dividends — sometimes exceeding 12 percent.  The stock is currently the best dividend payer in the S&P 500.  With dependable dividends and the ability to throw back free cash to investors, shareholders can’t ask for anything more.  In the first quarter alone, free cash flow amounted to $152 million and the company paid a dividend to shareholders representing 52 percent of that amount.  That’s $152 million Frontier won’t be spending to upgrade their service or have on hand to pay down debt.

For independent legacy landline providers like Frontier, reducing that dividend could spell disaster for the company’s stock price. Even investors understand this, which is why these kinds of cautionary notes are often attached to coverage about the company:

A cautionary note: telecoms companies with large fixed line exposure generally yield high dividends presently because investors do not believe their revenues and income levels are sustainable as people continue to substitute mobile phones for fixed lines.