Internal Ringtones need to be different

Anyone know how i can make internal ringtone different to calls from anyone of my trunks? ALl our phones are grandstream gxp2000 with the latest firmware. I only need two in total, one tone for any incoming call and one for any internal extension call. Thanks

I know this is late but the only thing I have found is to set 2 accounts per phone. One account is for incomming calls with the system ringtone and the 2nd account is for EXTENSION dialing with custom ringtone 1.
Anyone else have any suggesstions, I am all ears as this is an issue with one of my clients.

make internal the default ring, and set the alertinfo in the routing for calls coming from outside.