Can't establish a call from MC3810 toward 1750-2V with VoFR?

[hmcdavid]

Hi, MC3810 has IOS 12.1(22c) and 1750 has IOS 12.1(5)T. I've tried to upgrade the last to the same IOS but That IOS doesn't works with VoFR. Both are configured with vofr cisco. When I try to call sounds like the number doesn't exist instead vicerversa from 1750 toward MC3810 I could establish it. Both routers has 32/8 of memory. I've tried with anothers version but nothings works always the same. Anyone can tell me what exactly IOS version I need. Better If I shouldn't upgrade memory. I was looking for an exactly example but I can´t find it, Does VoFR CISCO works with a 1750-2V and MC3810? PLS, HELP ME ASAP

[thomas.chen]

Please check the Software advisor tool to find the IOS release required for particular Platform to run VoFR. May be it doesnt work with some particular Cisco IOS.

[hmcdavid]

I solved changing the codec on MC3810 since g729ar8 to g729r8. 1750 with IOS 12.1(5)T doesn't work with that codec.