Hi,
The following are good for small setups:
Cloud Options:
> Software Phone + head sets and a hosted VoIP provider such Gradwell or any good hosted
> Snom 300 Phones around (50-70 pounds) + VoIP Provider in cloud.
Onsite Options:
> Avaya IP Office 500 + Phones + SIP Trunks (expensive but never had one fail)
> Asterix + Phones + Sip Trunks (cheaper, works well if hardware is good and requires more setup)
Points to look out for:
> Firewall SiP ALG issues, most good firewalls will try to "fix" sip, you will need to make sure that ALG options are off or you have good support with vendor.