Code Sec 408(p) describes SIMPLE IRAs. Code Sec 402(g) defines the annual contribution limit; specifically, 402(g)(3)(D) includes elective contributions under 408(p)(2)(A)(i). 402(g)(1)(c) says the amount excluded from an individual's gross income also includes the "applicable dollar amount" under 414(v)(2)(B)(i). It further says that amount is "without regard to the treatment of the elective deferrals by an applicable employer plan under section 414 (v)" (which, among other impacts, means you ignore the qualifier in 414(v)(2)(B)(i) which applies at the plan level and just take the specific dollar amount from the paragraph).
The consequence is a weird disparity between the plans' limits and the individual's limits. An individual SIMPLE IRA can't let you make catch-up of more than $2,500. But you as an individual, using two separate SIMPLE IRA plans (of unrelated employers), can make $2,500 + $2,500 for a total of $5,000.
This fits w/ Denise Appleby's answer to the same question here:
http://www.investopedia.com/ask/answers/07/SIMPLE_IRA.aspAs several posters agreed above, it's extremely important that the companies not be related or else they likely count as one single employer and the limits then apply in aggregate.
EDIT: just caught this piece...
QUOTE (SeanF @ Apr 10 2009, 07:26 AM)

Thank you for your thoughts. He is part owner of each employer.
This gives you a major problem. See my last sentence above.