first, don't go for Aztech DSL305E. that modem is troublesome. there are many bad reports about this modem, especially when you try to save the configurations and restarting the modem. sometime it will erased the ROM, or write some garbage data on it and you have to go buy another modem.

second, go and buy any DSL modem that support internal router. this is good because you don't have to buy extra router for extra internet connection on the office. check with the seller whether the router support NAT and PAT (port fowarding).

good luck!