It may be 'fun' and all, but you have a potentially serious problem on your hands.
You seem to be basing your defense on the claim that the FAX was sent by a 'former partner' thereby relieving you of any responsibility. Sorry, but that won't hold up if the 'act' was done by the partnership and you are a responsible partner. And, if you (as a partnership) sent this FAX out in violation of state or federal laws, your partnership is liable.
Depending on the structure of this 'partnership', you could very well get stuck with a $3,000 judgment.
Also, in researching the Texas Statutes, I can only find a possible violation using TX CIV PRA & REM CODE, Chapter 143 ("HARMFUL ACCESS BY COMPUTER"), but that is contingent on actions that violate TX PENAL CODE, Chapter 33. A review of that chapter shows that it clearly pertains to computers, not FAX machines. So, no relevant Texas statutes:
Source:
http://www.capitol.state.tx.us/statutes/statutes.html
So, since you didn't tell us what basis is being claimed for the lawsuit against you, I assume the claim is a violation of 47 USC 227(b), which reads:
"(1) Prohibitions
It shall be unlawful for any person within the United States -
"(C) to use any telephone facsimile machine, computer, or other device to send an unsolicited advertisement to a telephone facsimile machine;"
Reading further, you will see that this same Code provides for actions:
"(3) Private right of action
A person or entity may, if otherwise permitted by the laws or rules of court of a State, bring in an appropriate court of that State -
(A) an action based on a violation of this subsection or the regulations prescribed under this subsection to enjoin such violation,
(B) an action to recover for actual monetary loss from such a violation, or to receive $500 in damages for each such violation, whichever is greater, or
(C) both such actions.
If the court finds that the defendant willfully or knowingly violated this subsection or the regulations prescribed under this subsection, the court may, in its discretion, increase the amount of the award to an amount equal to not more than 3 times the amount available under subparagraph (B) of this paragraph."
Source:
http://www4.law.cornell.edu/uscode/47/227.html
Looks to me like IF your partnership knowingly violated the law, a judgment could be rendered against the partnership. And if you are member of the partnership, depending on its structure, you could be liable.