Minimum IOS level for 2811 as PRI gateway

It has been a while since I did any heavy duty Cisco router config. Anybody know what the minimal IOS level requirement is for using a 2811 as a PRI gateway. The unit I have only has IP Base which is not letting me configure voice commands.

Here is a show hardware.

System image file is "flash:c2800nm-ipbase-mz.124-3f.bin"
Cisco 2811 (revision 53.51) with 251904K/10240K bytes of memory.
2 FastEthernet interfaces
24 Serial interfaces
1 Channelized T1/PRI port
DRAM configuration is 64 bits wide with parity enabled.
239K bytes of non-volatile configuration memory.
62720K bytes of ATA CompactFlash (Read/Write)

It’s not so much the version as the feature set.

You need: slot0:c3725-ipvoicek9-mz.124-25c.bin

This is 3725 code but you get the idea.

Feature set, that’s right. Like I said it has been a while since I have done a lot of Cisco stuff. I was a network admin for a fortune 50 some years ago.

50 years? Back in the SNA days?

It was a Fortune 50 company, very large. We had a lot of SNA and STUN and huge data centers filled with IBM mainframes.