Trefis members have created forecasts for two key drivers of

AT&T

(T) - Get Report

shares over the last week: Mobile CapEx (as a percentage of mobile gross profits) and mobile plans and phones gross profit margin.

Their forecasts suggest that the Mobile CapEx trends higher than the Trefis forecast, while the Mobile Plans & Phones Gross Profit Margin is in line with the Trefis forecast. These projections suggest a combined downside of around 6% for AT&T's stock.

Mobile Plans & Phones is the most valuable division, constituting

43% of the $38 Trefis price estimate for AT&T's stock

. In comparison, Internet & TV and Phone Landlines account for around 19% and 15%, respectively, of the stock. AT&T primarily competes with

Sprint Nextel

(S) - Get Report

and

Verizon

(VZ) - Get Report

in the mobile phones business.

Given that mobile plans and phones form the core business, AT&T's stock is quite sensitive to Mobile CapEx as a percentage of Mobile Gross Profits and Mobile Plans & Phones Gross Profit Margin.

The average of forecasts for Mobile CapEx as a percentage of Mobile Gross Profits created by Trefis members indicated a projected increase from about 22% in 2010 to nearly 26% by the end of the Trefis forecast period, compared to the baseline Trefis estimate of an increase from about 20% in 2010 to 22% by the end of the Trefis forecast period.

The member estimates imply a downside of 7% to the Trefis price estimate for AT&T's stock. In the past, Mobile CapEx as a percentage of Mobile Gross Profits has increased from 15% in 2007 to 18% in 2009.

You can drag the forecast trend-line above to express your own view, and see the sensitivity of AT&T's stock to Mobile CapEx as a percentage of Mobile Gross Profits.

Our

complete analysis for Mobile CapEx as a percent of Mobile Gross Profits is here

.

The average of forecasts for Mobile Plans & Phones Gross Profit Margin created by Trefis members indicated a projected decrease from about 59% in 2010 to about 53% by the end of the Trefis forecast period, mostly in-line with the Trefis forecast.

The member estimates imply an upside of 1% to the Trefis price estimate for AT&T's stock. In the past, Mobile Plans & Phones Gross Profit Margin has decreased from 70% in 2003 to about 60% in 2009.

You can drag the forecast trend-line above to express your own view, and see the sensitivity of AT&T's stock to Mobile Plans & Phones Gross Profit Margin.

Our

complete analysis for AT&T's stock is here

.

Trefis

is a financial community structured around trends, forecasts and insights related to some of the most popular stocks in the U.S.