SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* EnerTech Capital Partners II, L.P. (Last) (First) (Middle) 700 BUILDING 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol ARBINET THEXCHANGE INC [ ARBX ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 12/21/2004
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	12/21/2004		C		2,322,124	A	(1)	2,322,124	D(2)
Common Stock	12/21/2004		C		88,577	A	(1)	88,577	D(2)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series D-1 Convertible Preferred Stock	(1)	12/21/2004		C			4,979,613	(1)	(1)	Common Stock	311,225	(1)	0	D(2)
Series D-1 Convertible Preferred Stock	(1)	12/21/2004		C			25,591,553	(1)	(1)	Common Stock	1,599,472	(1)	0	D(2)
Series D-1 Convertible Preferred Stock	(1)	12/21/2004		C			6,582,839	(1)	(1)	Common Stock	411,427	(1)	0	D(2)
Series D-1 Convertible Preferred Stock	(1)	12/21/2004		C			189,950	(1)	(1)	Common Stock	11,871	(1)	0	D(3)
Series D-1 Convertible Preferred Stock	(1)	12/21/2004		C			976,205	(1)	(1)	Common Stock	61,012	(1)	0	D(3)
Series D-1 Convertible Preferred Stock	(1)	12/21/2004		C			251,107	(1)	(1)	Common Stock	15,694	(1)	0	D(3)

1. Name and Address of Reporting Person* EnerTech Capital Partners II, L.P. (Last) (First) (Middle) 700 BUILDING 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ECP II Management, L.P. (Last) (First) (Middle) 700 BUILDING, 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ECP II Interfund, L.P. (Last) (First) (Middle) 700 BUILDING, 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* ECP II Management, LLC (Last) (First) (Middle) 700 BUILDING, 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Ungerer Scott B (Last) (First) (Middle) 700 BUILDING, 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* KEITH ROBERT E JR (Last) (First) (Middle) 700 BUILDING, 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* DENINO MARK J (Last) (First) (Middle) 700 BUILDING, 435 DEVON PARK DRIVE (Street) WAYNE PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Lincoln David F (Last) (First) (Middle) 700 BUILDING, 435 PARK DRIVE, (Street) WAYNE, PA 19087 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. Each share of Series D-1 Convertible Preferred Stock, Series E Convertible Preferred Stock and Series E-1 Convertible Preferred Stock automatically converted into common stock reflecting all stock splits and other adjustments pursuant to the Issuer's Certificate of Incorporation, as amended, upon the closing of the Issuer's initial public offering of common stock.

2. See Exhibit 99.1. Shares are held by EnerTech Capital Partners II L.P. ("ECP II LP"). ECP II Management L.P., the general partner of ECP II LP, ECP II Management LLC, the general partner of ECP II Management L.P., and Robert E. Keith, Jr., Mark J. DeNino, Scott B. Ungerer, William G. Kingsley, and David F. Lincoln, the members of the executive board of ECP II Management LLC, may be deemed to share voting and dispositive power over the shares held by ECP II LP. Such persons and entities disclaim beneficial ownership of shares held by ECP II LP except to the extent of any pecuniary interest therein.

3. See Exhibit 99.1. Shares are held by ECP II Interfund L.P. ("ECP II Interfund"). ECP II Management LLC, the general partner of ECP II Interfund, and Robert E. Keith, Jr., Mark J. DeNino, Scott B. Ungerer, William G. Kingsley, and David F. Lincoln, the members of the executive board of ECP II Management LLC, may be deemed to share voting and dispositive power over the shares held by ECP II Interfund. Such persons and entities disclaim beneficial ownership of shares held by ECP II Interfund except to the extent of any pecuniary interest therein.

	/s/ Pamela Strisofsky By Pamela Strisofsky as Attorney-in-Fact	12/21/2004
	** Signature of Reporting Person	Date
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