Ken,

It is better to address this question directly to United agent serving Manhattan (I listed all of them below). You should know though that if your shipment is small enough to fit a regular truck (usually up to 24') it will most probably be picked up with a local truck and then transferred to the United interstate truck for further hauling. Larger shipments could be picked up directly by an iterstate truck, but this should be organized directly with their agent.

Here is the list of United Vanlines agents in Manhattan as of today (taken from United Vanlines website):

LIBERTY MOVING & STORAGE CO.
304 EAST 65TH STREET,SUITE 21C
NEW YORK CITY, NY 10021
Telephone: (212) 223-6440
Toll Free: (800) 640-4487

MORGAN & BROTHER MANHATTAN STORAGE CO., INC.
434 EAST 91ST STREET
NEW YORK CITY, NY 10028
Telephone: (212) 996-5201
Fax: (212) 369-8512
Toll Free: (800) 969-6674

NASSAU MOVING & STORAGE, INC.
19 WEST 21ST STREET SUITE 606
NEW YORK CITY, NY 10010
Telephone: (212) 741-8166
Fax: (212) 741-8076

VICTORY VAN LINES, INC.
25 WEST 43RD STREET
NEW YORK CITY, NY 10036
Fax: (212) 302-1196