Is it possible to connect outgoing and ingoing calls as a conference?

I have a Panasonic KX-TG5631 and Vonage phone service. I am able to connect 2 other caller into conference mode however the catch is that I have to call them

I have a cell phone with Sprint which allows me to connect both incoming and outgoing calls into conference mode.

Does anybody know of any phone that would allow me to connect outgoing/incoming calls into a conference?

I would have several uses for the use like this and it would be really helpful as I run a business and I do conference calls several times a day. Anybody know if this is possible with a cordless phone similiar to the Panasonic we are using, or does the change need to be from our service provider to allow incoming/outgoing calls to conference?

I am not aware of a phone that will allow that, however conferencing services allow you to both dial out and receive conference calls at any time as well as send e-mails to potential participants to join a conference call if you can't get them via phone

it is possible on some phones take the iphone for example u can do that but with your phone i dont know if its possible