Just got MeContacts and it gives you a grid of 24 squares to allocate to a contact, then you can add extra grids by the look of things. In the menu function it then gives you the ability to group sms, presumably to all the people on that particular grid. I don't know how many grids it will let you have cos I have only got the one on the go for my most used contacts. Its a freebie so give it a go!