Swedish telecom equipment maker Ericsson on Wednesday reported a 73-percent slide in its fourth quarter net profit on weak mobile network sales, sending its share price into freefall.

For the period from October to December, Ericsson registered a net profit of 1.15 billion kronor (130.8 million euros, $170 million), compared with 4.32 billion a year earlier.

Sales in the quarter amounted to SEK 63.7 (62.8) b., was up 1% year-over-year and 15% sequentially.

Sales for comparable units, adjusted for currency exchange rate effects and hedging, increased 6% year-over-year. The sequential increase is mainly related to strong growth in services.

In 2011, sales amounted to SEK 226.9 (203.3) b., up 12%, driven by strong demand for mobile broadband along with network rollout services. Sales in 2011 for comparable units, adjusted for currency exchange rate effects and hedging, increased 19%.

Software represented 23% (24%), hardware 40% (37%) and services 37% (39%) of total sales in 2011.

In the fourth quarter 2011 restructuring charges of SEK 0.7 b. were included, while the last quarter 2010 exclude restructuring charges of SEK 1.7 b. Total restructuring charges for 2011 amounted to SEK 3.2 (6.8) b. excluding joint ventures. For 2012, restructuring charges are estimated to approximately SEK 4 b. and the main part of activities expected in the first half of 2012.

Gross margin in the quarter was down year-over-year to 30.2% (36.6%), and down from 35.0% sequentially. As previously communicated, network modernization projects in Europeaccelerated in the quarter and together with a higher proportion of coverage projects, as well as an all time high Global Services share of 42%, impacted gross margin negatively. Including restructuring charges fourth quarter 2010 gross margin amounted to 34.7%.

In 2011, gross margin declined from 38.2% to 35.1% due to higher share of coverage projects, network modernization projects in Europe and 3G rollouts in India.

All modernization projects that Ericsson has won have started by the fourth quarter 2011. The network modernization projects in Europe, with their lower margins, fully impacted the fourth quarter. Since average project duration is expected to be 18-24 months, the impact is expected to prevail for a couple of more quarters.

Total operating expenses amounted to S