The answer given by the carrier doesn't seem right but more information / clarification is needed to understand why they said that:
- What device is trying to ping the gateway? Is it the TA900 itself (i.e. you're logged into the TA900 CLI and trying to ping the gateway) or is it a device connected behind the TA900 (like a PC)?
- How many IP interfaces do you have configured on the TA900 (WAN / LAN or just WAN)
- Are they public or private?
Generally speaking, if you have a data T1 circuit with PPP and private IP subnet on it, then when logging into the TA908 you *should* be able to ping your own WAN gateway IP (even if it's private), unless the carrier has blocked PING requests on their side for security reasons.
If you have a computer connected to the TA900 via Ethernet and it's using public IPs, then you will not be able to ping the T1 WAN gateway (because it's private), but you will be able to ping the gateway of the public IP subnet you've been assigned by your provider.
Hope this helps,