Well,
Prima has 2 offers: "PrimaVoceMobile" (only postpaid, 5€/month, free roaming in Italy on Vodafone net) and "PrimaVoceCasa" (only postpaid, no roaming, no monthly fee... officially is an offer for landline, but San Marino Telecom offers the service by GSM/UMTS services with a simcard not allowed to international roaming):
the first one is interesting expecially if you buy one of 2 bundles (see
http://www.prima.sm/default.asp?id=333 , Super20 or Super50), the second one imho is great (more than "VodafoneCasa" or "MaxxiTim Casa", the 2 italian option for using the landline service from a mobile), take a look:
http://www.prima.sm/default.asp?id=326
1= Set up fee 0,12€
*= Without set up fee.