[Effendi]

Ok, in St.Petersburg you have 4 operators, the 3 national ones (Megafon, Beeline, MTS) plus Tele2 which cannot be considered "national" yet, but it's expanding. BTW it's the crappiest one...

I suppose you are going to Veliky Novgorod (Великий Новгород), which is not far from St.Petersburg but it's out of the "Leningrad Region", so if you buy a Russsian simcard based in St.Petersburg/Leningrad Region you'll go roaming in Novgorod, but rates are never expensive in any case. I think MTS, Megafon and Beeline all cover Novgorod without any problem.

Using Travelsim you should have no problems to roam both in St.Petersburg and Veliky Novgorod.