LightSquared added some muscle to its top brass today when it appointed an executive who oversaw the $70 billion merger between Sprint and Nextel as its new CFO.

Marc Montagner takes the place of Michael Montemarano, who "mutually decided to leave," a spokeswoman for LightSquared said.

The appointment of Montagner comes just days after Sprint granted LightSquared a 30-day extension on a Dec. 31 deadline to get FCC approval for the launch of its LTE network, which has been delayed by ongoing concerns over GPS interference.

LightSquared hired Sprint last summer to install LTE equipment capable of hosting services running on the L-band spectrum it wants to use for its network. FCC approval for the network was a condition of the contract. LightSquared already has made some payments to Sprint for the deal, valued at $9 billion in cash over the next 11 years.

Montagner will have to guide LightSquared's finances as the company continues to battle the FCC to get clearance for its hybrid satellite-terrestrial LTE network, which it wants to sell on a wholesale basis to outside companies interested in offering mobile broadband service.

LightSquared's primary backer, Philip Falcone's hedge fund Harbinger Capital Partners, has seen the value of its portfolio drop over the past few quarters, and many investors have questioned the fund's $2.9 billion gamble on LightSquared.

Montagner most recently was a managing partner at Dupont Circle Partners, an advisory firm specializing in mergers and acquisitions in the media, technology and telecommunications industries.

He also held a post in sales and marketing at SkyTerra, which later became part of LightSquared. At SkyTerra, Montagner worked on regulatory, technical and financial issues related to repurposing the company's satellite spectrum for use in land-based communications.

During his time at Sprint, Montagner was in charge of all merger and acquisition activities, including the 2005 merger with Nextel.

Montagner's experience with SkyTerra's efforts to reuse its satellite spectrum could prove valuable in LightSquared's fight to get the go-ahead for its network. LightSquared continues to insist it can resolve issues with GPS despite mounting government evidence that its base stations will have an impact on some receivers, even if the service runs in spectrum farther away from GPS bands, a mitigation measure suggested by the company.

Many in the GPS industry and federal government say LightSquared's network is an unacceptable threat to the satellite service, which is critical to landing planes, guiding missiles and sailing ships.

The FCC has kept quiet in recent months about the ongoing controversy about LightSquared's network but has said it will not give the company the green light until all interference issues are addressed.