[aaronpk]

Their terms of service also prohibit apps from using "gram" in the name.

[taytus]

This is correct for applications using IG's API. This is not the case for statimgram.

[CaveTech]

Using private API's while also infringing on their terms, basically guaranteeing that your service will be blocked the minute it has any type of traction.

[ceejayoz]

Your bigger concern should probably be Facebook's trademark lawyers.