As of Simple Invoices 2010.2, Simple Invoices now supports 'Invoice numbering groups'
Invoices numbering groups allow you to have multiple number ranges based on invoice preferences. This was for examples you can have quotes 1,2,3,4,5 and invoices 1,2,3,4,5 as well
By default all types of invoices (estimates, quotes, etc. ) in Simple Invoices share the same invoice numbering range
Simple Invoices also supports the possibility for setting multiple invoice numbering ranges
Each 'Invoice Preference' can belong to its own invoice numbering range or belong to that of another Invoice Preferene
If an Invoice Preference its own then it increments in its own range (ie Invoices 1,2,3,4,5)
but if an Invoice Preference shares the same invoice number group as another preference then they share the numbering range