Orbtalk have a range of SIP trunk products that work with the AltiGen Max Range
The MAX1000 is a premium full-featured VoIP phone system designed for branch offices and locations with up to 48 users with support for such features as SIP trunking, Meet-me conference bridge capability with scheduling application, On-demand Voice Recording, 4500 hours of voice mail storage, ExtensionAnywhere™ mobility and many other features in a single-box appliance.
AltiGen has also released the MAX2000 VoIP phone system. It’s an enhancement to the MAX1000 and MAX1000R platforms and has support for up to 100 users.