Travel Technology - iPhone 4 v. 4s for VOIP Over 3g

I have ATT's iPhone International Plan which gives me unlimited worldwide data, much like iPhone trip. I doubt ATT will let me carry this plan forward to an LTE device from what I am seeing with people who have the Android equivalent.

If I pop $540 for an ATT unsubsidized iPhone 4s, will it significantly help with VOIP over 3g? I can get it to work, but I have to prep for the call. Close the other apps to make sure I have enough memory and thinking about my calling situation. I know HSPA+ isn't going to help me on a train, but I'm wondering whether the slightly faster network (I know it ain't 4g, but HSPA+ has increasing support) coupled with the faster processor might give me an edge.

Opinions?

I have ATT's iPhone International Plan which gives me unlimited worldwide data, much like iPhone trip. I doubt ATT will let me carry this plan forward to an LTE device from what I am seeing with people who have the Android equivalent.

If I pop $540 for an ATT unsubsidized iPhone 4s, will it significantly help with VOIP over 3g? I can get it to work, but I have to prep for the call. Close the other apps to make sure I have enough memory and thinking about my calling situation. I know HSPA+ isn't going to help me on a train, but I'm wondering whether the slightly faster network (I know it ain't 4g, but HSPA+ has increasing support) coupled with the faster processor might give me an edge.

Opinions?

The faster processor can't hurt and probably a slightly better communications chip in the newer phone but its a lot of money for something that might be only marginally better.