I'm no expert on these Best Buy options, never bought a phone through them but this is in the fine print once you select that phone:
Except as follows, your current Verizon price plan and features will not be changed with this transaction. Each device added or upgraded to your account will incur a Monthly Line Access Fee which may vary based upon your contract or device payment enrollment.
Also, the $1.99 phone is the regular Droid Z, not the Force. Not that there is anything wrong with that, it's a really nice phone; but the shatter proof screen and larger battery may be worth the extra $$ to get the Force.