Strong December demand boosts Spirent's 4th-quarter orders

* Q4 orders up 13 pct to about $147 mln

* Sees Q4 sales at top end of view, 10 pct rise in FY sales

* Verizon Communications (Xetra: 868402 - news) now largest customer-CEO

* Americas orders up 7 pct in 2014, Asia-Pacific up 5 pct

* Shares (Dusseldorf: DI6.DU - news) rise as much as 14 pct, among top LSE gainers (Adds CEO and CFO comments)

By Noor Zainab Hussain

Jan 8 (Reuters) - Spirent Communications Plc (Other OTC: SPMYY - news) , a British telecoms testing services provider, said fourth-quarter orders exceeded its expectations, helped by strong demand from customers in the United States and Asia-Pacific in December.

Shares of the company, which tests ethernet networks, 3G and 4G wireless networks and devices, rose as much as 14 percent on Thursday, making them one of the top gainers on the London Stock Exchange.

Verizon Communications Inc overtook AT&T Inc (Sao Paolo: ATTB34.SA - news) and Cisco Systems Inc (Xetra: 878841 - news) as Spirent's No.1 customer, as the telecoms company's recent acquisitions helped keep orders steady in an industry that was cutting spending, Chief Executive Eric Hutchinson told Reuters.

Hutchinson said Spirent also benefited from more business from Samsung Electronics Co Ltd and from service providers and equipment manufacturers in China.

The company, which had warned in November that weak market conditions in the third quarter would stay for the rest of 2014, estimated full-year 2014 revenue at about $455 million, a 10 percent jump from a year earlier.

Spirent said on Thursday that fourth-quarter order intake rose nearly 13 percent to about $147 million, with revenue of about $124 million, at the upper end of its expectations.

Orders from the Americas grew 7 percent in the year, while those from the Asia-Pacific region rose 5 percent, Chief Financial Officer Rachel Whiting told Reuters.

The United States accounted for 50 percent of Spirent's 2013 revenue, while Asia-Pacific contributed about 35 percent.

AT&T's said in November it would cut spending in 2015, one of many such decisions by telecom companies over the past few months in an industry grappling with potential merger activity and assessing new technology deployments.

CEO Hutchinson said orders from two large clients and some equipment makers had reduced by as much as $30 million in 2014.

Spirent shares were up 10.8 percent at 87.25 pence at 1320 GMT. (Editing by Gopakumar Warrier and Savio D'Souza)