Hi there,
You won't be able to setup a distinctive ring between internal and external calls.
What you can do is configure a distinctive ring based on the extension you're using on the phone.
The distinctive ring configuration on the phone, refers to the Cadence, which can be applied to each ringtone that you have on the phone.
<Ring1 ua="na">n=Sunrise;w=file://Sunrise.rwb;c=1</Ring1>
<Ring2 ua="na">n=Chirp 1;w=file://chirp1.raw;c=1</Ring2>
<Ring3 ua="na">n=Chirp 2;w=file://chirp2.raw;c=1</Ring3>
<Ring4 ua="na">n=Delight;w=file://Delight.rwb;c=1</Ring4>
<Ring5 ua="na">n=Evolve;w=file://Evolve.rwb;c=1</Ring5>
<Ring6 ua="na">n=Mellow;w=file://Mellow.rwb;c=1</Ring6>
<Ring7 ua="na">n=Mischief;w=file://Mischief.rwb;c=1</Ring7>
<Ring8 ua="na">n=Reflections;w=file://Reflections.rwb;c=1</Ring8>
<Ring9 ua="na">n=Ringer;w=file://Ringer.rwb;c=1</Ring9>
<Ring10 ua="na">n=Ascent;w=file://Ascent.rwb;c=1</Ring10>
<Ring11 ua="na">n=Are you there;w=file://AreYouThereF.raw;c=1</Ring11>
<Ring12 ua="na">n=Chime;w=file://Chime.raw;c=1</Ring12>
By default, all ringtones are using Cadence 1 as above c=1
<Cadence_1 ua="na">60(2/4)</Cadence_1>
<Cadence_2 ua="na">60(.3/.2,1/.2,.3/4)</Cadence_2>
<Cadence_3 ua="na">60(.8/.4,.8/4)</Cadence_3>
<Cadence_4 ua="na">60(.4/.2,.3/.2,.8/4)</Cadence_4>
<Cadence_5 ua="na">60(.2/.2,.2/.2,.2/.2,1/4)</Cadence_5>
<Cadence_6 ua="na">60(.2/.4,.2/.4,.2/4)</Cadence_6>
<Cadence_7 ua="na">60(4.5/4)</Cadence_7>
<Cadence_8 ua="na">60(0.25/9.75)</Cadence_8>
<Cadence_9 ua="na">60(.4/.2,.4/2)</Cadence_9>
Thanks