This doco comes in the IB6's main dir; here's an excerpt:
**********
7. DISCLAIMER OF WARRANTY.
COVERED CODE IS PROVIDED UNDER THIS LICENSE ON AN "AS IS'' BASIS, WITHOUT
WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, WITHOUT
LIMITATION, WARRANTIES THAT THE COVERED CODE IS FREE OF DEFECTS,
MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE OR NON-INFRINGING. THE ENTIRE
RISK AS TO THE QUALITY AND PERFORMANCE OF THE COVERED CODE IS WITH YOU.
SHOULD ANY COVERED CODE PROVE DEFECTIVE IN ANY RESPECT, YOU (NOT THE INITIAL
DEVELOPER OR ANY OTHER CONTRIBUTOR) ASSUME THE COST OF ANY NECESSARY
SERVICING, REPAIR OR CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN
ESSENTIAL PART OF THIS LICENSE. NO USE OF ANY COVERED CODE IS AUTHORIZED
HEREUNDER EXCEPT UNDER THIS DISCLAIMER.
8. TERMINATION.
8.1. This License and the rights granted hereunder will terminate
automatically if You fail to comply with terms herein and fail to cure such
breach within 30 days of becoming aware of the breach. All sublicenses to
the Covered Code which are properly granted shall survive any termination of
this License. Provisions which, by their nature, must remain in effect
beyond the termination of this License shall survive.
**********

So, what warranty could be void, please? In the case of the current IB6,
simply NONE. So, let's take a peek at license.txt from IB5.6:
**********
LIMITED WARRANTY AND LIMITATION OF LIABILITY
InterBase warrants that the Software, as
updated and when properly used, will perform
substantially in accordance with its
accompanying documentation, and the Software
media will be free from defects in materials
and workmanship, for a period of ninety (90)
days from the date of receipt. Any implied
warranties on the Software are limited to
ninety (90) days. Some states or
jurisdictions do not allow limitations on
duration of an implied warranty, so the above
limitation may not apply to you.

InterBase's and its suppliers' entire
liability and your exclusive remedy shall be,
at InterBase's option, either (a) return of
the price paid, or (b) repair or replacement
of the Software that does not meet the
Limited Warranty and which is returned to
InterBase with a copy of your receipt. DO NOT
RETURN ANY PRODUCT UNTIL YOU HAVE CALLED THE
INTERBASE CUSTOMER SERVICE DEPARTMENT AND
OBTAINED A RETURN AUTHORIZATION NUMBER. This
Limited Warranty is void if Software fails as
a result of accident, abuse, or
misapplication. Any replacement Software
will be warranted for the remainder of the
original warranty period or thirty (30) days,
whichever is longer. Outside the United
States, neither these remedies nor any
product support services offered by InterBase
are available without proof of purchase from
an authorized non-U.S. source.
**********
In other words, for people that have been using IB4 and IB5 for some months
(probably most of clients), the license has expired already. So, again,
what's license?
I know IB-architect is off-topic to discuss this, hence I used IBDI and
only CC'ed the former for only one time. At least I won't push this anymore
in IB-Architect. The threaten "any other patch will void the warranty" seems
more like typical PR regarding IB in the last 9 years: 90% bullshit.
You should decide whether the IBPhoenix or the Borland patch is better for
you, based on what those patches do to your binaries (technical
implications) rather than based on legal implications, as you can see. Some
of my clients that acquired IB4 three years ago (and are still using it)
wouldn't be much concerned to void a license that died in a natural way 3
months after they acquired the product.

C.
---------
Claudio Valderrama C.
Ingeniero en Informática - Consultor independiente
http://www.cvalde.com