Group Texting Question

I have a simple group of contacts, 9 people total. When I enter the group into the" to" field of a.text message it will say the group name and then" (6/9)". All entries in the group have associated phone numbers and I can't find any differences between them. Why does the Atrix only want to send texts to 6 of the 9? Thanks.
SH92

Well nevermind. The numbers that the phone wouldn't send to through the group feature were listed as work not mobile numbers. Strangely it has no problem sending texts to those.numbers on their own (while still listed as work numbers). Problem solved. ;-)