Since T-Mobile "upgraded" their system to 4G LTE the signal strength in the house has dropped by more than 50%. I must use WIFI in the house. The phone is a Samsung Galaxy SII. My gal has the same phone with the same provider. Her's never switched to LTE and she maintains a full signal in the house....go figure.
Regardless of the phone you get using WIFI in a weak cell network area is the way to go. Almost all modern phones have the WIFI option.
I think (think) that this has something to with the S2 (I have it) not being an LTE device, it will get 4G Wimax and maybe HSPA (again, not sure) If you had a newer LTE capable device, things might be very different?