VOIP options/recommendations

Hi there

Does anyone have recommendations for VOIP systems & installers. Ive seen the nightmare when a VOIP install goes bad, very bad (no ph's for 3 weeks)

Its a Ak CBD office, 10 users, SBS2011 based network, Sonicwall firewall, ADSL only at this stage . Management are simply looking to save money on phone bills. Should they just go with telecom/voda or though a 3rd party system . Is VOIP over ADSL just asking for issues ?