Exhibit 10.28

As
of September 3, 2003

Gene
Musselman
Groot Haesebroekseweg 37
Wassenaar, The Netherlands 2243 ED

|Re: |  | Addendum to employment letter agreement among UnitedGlobalCom, Inc., United Pan-Europe Communications N.V. and yourself dated December 4, 2002 ("Employment Agreement")
|--- |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------

Dear
Gene:

This
letter agreement constitutes an addendum to the Employment Agreement. Subject to the terms and conditions set forth below and your acceptance of such terms and conditions, the
Employment Agreement is modified as follows:

1.     Title:Your title will be changed from the current title to "President and Chief Operating Officer of UPC Broadband
Division" of UGC Europe, Inc. ("UGCE").

2.     Term:The term of the Employment Agreement is extended to December 31, 2007.

3.     Bonus:The Company has paid you a bonus in the amount of $500,000 (the "Bonus"). The Bonus will not be tax equalized under
the Company's tax equalization policy.

4.     SARs Grant:On October 7, 2003, the Compensation Committee of UGCE approved a grant of stock appreciation rights
("SARs") to you based on the following criteria:



5.     Minimum Gain:UnitedGlobalCom, Inc. ("United") agrees to ensure that during the term of your employment and upon
full vesting and exercise of the SARs, you will realize a pre-tax Gain of at least one million dollars ($1,000,000) (the "Guarantee"), subject to the following:



---



6.     Termination of Employment:If your employment with United is terminated, either voluntarily by you or by United for cause,
all vesting of the SARs stops as of the date of termination of employment.



Except
as modified by this addendum, all other terms and conditions of your Employment Agreement remain in full force and effect, and the Employment Agreement and this addendum contains
the parties entire agreement with respect to your employment.

2

---

Please
indicate your acceptance to the above terms and conditions by signing below and returning one executed original to me, along with the attached notices.

|UNITEDGLOBALCOM, INC.
[Employer]                     |  | AGREED AND ACCEPTED:                                                   
|---------------------------------------------------- |  | -----------------------------------------------------------------------
|By:                                                  |  | /s/MICHAEL T. FRIESMichael T. Fries
President & Chief Executive Officer
|Date:                                                |  | March 11, 2004                                                         
|UNITED PAN-EUROPE COMMUNICATIONS N.V.
[Host Company]
|By:                                                  |  | /s/ANTON TUIJTENAttorney-In-Fact                                       
|Date:                                                |  | March 11, 2004                                                         
|By:                                                  |  | /s/CHARLES H.R. BRACKENAttorney-In-Fact                                
|Date:                                                |  | March 11, 2004                                                         

3

---

QuickLinks