Exhibit 10.10

Execution Copy

THIS NOTE AND THE SECURITIES ISSUABLE UPON THE CONVERSION HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ ACT ” ), OR ANY STATE SECURITIES LAWS AND MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR TRANSFERRED ABSENT SUCH REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT AND APPLICABLE STATE LAWS.  

THIS NOTE WAS ISSUED WITH ORIGINAL ISSUE DISCOUNT ( “ OID ” ) FOR UNITED STATES FEDERAL INCOME TAX PURPOSES.  UPON REQUEST, THE COMPANY WILL PROMPTLY MAKE AVAILABLE TO A HOLDER OF THIS NOTE INFORMATION REGARDING THE ISSUE PRICE, THE AMOUNT OF OID, THE ISSUE DATE AND THE YIELD TO MATURITY OF THIS NOTE.  HOLDER SHOULD CONTACT THE CHIEF FINANCIAL OFFICER AT IRIDIUM HOLDINGS LLC, 6707 DEMOCRACY BLVD, SUITE 300, BETHESDA, MARYLAND 20817.

IRIDIUM HOLDINGS LLC

CONVERTIBLE SUBORDINATED PROMISSORY NOTE

FOR VALUE RECEIVED , Iridium Holdings LLC, a Delaware limited liability company (the “ Company ”), promises to pay to Greenhill & Co. Europe Holdings Limited, an English corporation (“ Greenhill ”), or its registered assigns, the principal amount of twenty-two million nine hundred thousand dollars (U.S. $22,900,000), on the Maturity Date, together with accrued interest at the Interest Rate (as defined below), such interest to accrue until the unpaid principal balance is paid in full.  All unpaid principal of this Note, together with any then unpaid and accrued interest and other amounts payable hereunder, shall be due and payable on the seventh anniversary of the date hereof (the “ Maturity Date ”).

The following is a statement of the rights of the Holder and the conditions to which this Note is subject, and to which the Holder, by the acceptance of this Note and the Company, by the issuance of this Note, agree:

1.

Definitions .

As used in this Note, the following capitalized terms have the following meanings:

(a)

“ Additional Common Units ” shall mean all Common Units issued (or, pursuant to Section 8(e), Section 8(h) or Section 8(i), deemed to be issued) by the Company after the Original Issue Date, other than

(i)

Common Units issued (A) pursuant to any bona fide acquisition of assets or operating business by the Company or any bona fide merger or business combination involving the acquisition by the Company of assets or operating business which has been approved by its Board of Directors; provided that any such transaction is at arms-length terms, (B) in connection with any pro rata distribution or split of Common Units in respect of which adjustment has been made pursuant to Section 8(g), (C) to financial institutions or commercial lenders in connection with commercial credit

arrangements, equipment financings or similar transactions, or (D) for commercial reasons and not capital-raising reasons, to potential or existing trade partners or service providers providing trade enabling services; provided that the aggregate Fair Market Value, in each case as determined at the time of issuance, of all Common Units issued pursuant to clauses (C) and (D) hereof may not exceed $15 million;

(ii)

up to30,000 Common Units (including any such Common Units which are repurchased) issued pursuant to the Company’s equity incentive plans; and

(iii)

Common Units issued in connection with any event for which adjustment is made pursuant to Section 8(h) hereof.

(b)

“ Affiliate ” means, with respect to any Person, any other Person directly or indirectly controlling, controlled by, or under common control of such Person.

(c)

“ Business Day ” means any day except a Saturday, Sunday or other day on which commercial banks in the City of New York are authorized by law to close.

(d)

“ Change of Control ” means the acquisition, directly or indirectly, by any Person who as of the date hereof does not control at least 25% of the Common Units, of the beneficial ownership (as defined in Rule 13d-3 promulgated under the Securities Exchange Act of 1934) in the Common Units representing more than 50% of all outstanding Common Units at such time.

(e)

“ Class A Units ” shall have the meaning set forth in the LLC Agreement.

(f)

“ Class B Units ” shall have the meaning set forth in the LLC Agreement.

(g)

“ Common Units ” or “ Units ” shall mean either (i) Class A Units or Class B Units or (ii) both Class A Units and Class B Units taken together.

(h)

“ Conversion Date ” shall have the meaning set forth in Section 8(d)(i).

(i)

“ Convertible Securities ” shall mean any evidences of indebtedness, shares of capital stock or other securities directly or indirectly convertible into or exchangeable for Common Units (other than the Note and the Common Units).

(j)

“ Event of Default ” has the meaning given in Section 5 hereof.

(k)

“ Fair Market Value ” as of any date means the fair market value as of such date as determined in good faith by the Board of Directors; provided that if the Holder objects to such determination, the Board of Directors shall retain an independent appraiser of national reputation reasonably satisfactory to the Holder in order to determine such fair market value, and such appraiser’s determination of the fair market value shall be binding hereunder (and the fees and expenses of such appraiser shall be borne equally by the Company and the Holder).

(l)

“ Holder ” means Greenhill and any other Person or Persons who shall at the time be the registered holder of this Note.

(m)

“ Initial Public Offering ” means any offering of the common equity securities of the Company (or its successor) to the public which results in net proceeds of at least $100 million pursuant to an effective registration statement under the Securities Act of 1933, as then in effect.

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(n)

“ Interest Rate ” means 0% initially and, six months after the issuance date, 5% per annum.

(o)

“ LLC Agreement ” means the Amended and Restated Limited Liability Company Agreement of Iridium Holdings LLC.

(p)

“ Lien ” means with respect to any property or asset, any mortgage, lien, pledge, charge, security interest, encumbrance or other adverse claim of any kind in respect of such property or asset.

(q)

“ Note Payment Amount ” means, as of any Business Day, with respect to this Note, the aggregate unpaid Principal Amount outstanding plus the aggregate amount of accrued but unpaid interest with respect to the Note.

(r)

“ Note Purchase Agreement ” means the note purchase agreement among the Company and Greenhill dated as of September 22, 2008.

(s)

“ Options ” mean rights, options or warrants to subscribe for, purchase or otherwise acquire Common Units or Convertible Securities.

(t)

“ Original Issue Date ” shall mean the date of the issuance of this Note.

(u)

“ Person ” means an individual, corporation, partnership, limited liability company, association, trust or other entity or organization, including a government or political subdivision or an agency or instrumentality thereof.

(v)

“ Principal Amount ” means $22,900,000.

(w)

“ Termination Event ” shall mean the termination of the Transaction Agreement pursuant to the terms thereof.

(x)

“ Transaction Agreement ” means the Transaction Agreement dated as of September 22, 2008 among the Company, GHL Acquisition Corp. and certain other parties.

2.

Interest .   Interest shall be calculated on the principal amount and accrue at a rate per annum equal to the Interest Rate, compounded quarterly and computed on the basis of the actual number of days elapsed and a year of 365 days.  Interest will not be paid until the date the Note is repaid or redeemed as provided in Section 3(a) or Section 7, as applicable.

3.

Payment .

(a)

Payment of the Note .  Subject to earlier conversion or repayment thereof pursuant to Section 7 or Section 8 hereof, the outstanding principal and all accrued interest on this Note shall be due and payable in full on the Maturity Date.  This Note will not be prepayable at the option of the Company.

(b)

Method of Payments .

(i)

Except to the extent otherwise provided herein, each payment by the Company of principal and interest owing under this Note shall be made in dollars in immediately available funds, without deduction, set-off or counterclaim, not later than 2:00 p.m. New York City Time

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on the date on which such payment shall become due by wire transfer to such account(s) as the Holder may notify the Company in writing.

(ii)

Notwithstanding anything to the contrary contained herein, if any due date under this Note would otherwise fall on a day that is not a Business Day, such date shall be extended to the next succeeding Business Day, and interest shall be payable for any principal so extended for the period of such extension.

4.

Notice of Defaults .   Promptly upon (but in no event later than three (3) Business Days after) the occurrence thereof, the Company will provide the Holder written notice of the occurrence of (i) any Event of Default hereunder or (ii) any event or circumstance which, with the giving of notice, passage of time, or both, will constitute an Event of Default.

5.

Events of Default and Right to Cure .   The occurrence of any of the following shall constitute an “ Event of Default ” under this Note:

(a)

Failure to Pay Principal or Interest . The Company fails to make a payment, when due, of any principal or interest due on this Note and, in the case of interest, such default contin