  Let $C_c^{*}(\mathbb{N}^{2})$ be the universal $C^{*}$-algebra generated by a
semigroup of isometries $\{v_{(m,n)}: m,n \in \mathbb{N}\}$ whose range
projections commute. We analyse the structure of KMS states on
$C_{c}^{*}(\mathbb{N}^2)$ for the time evolution determined by a homomorphism
$c:\mathbb{Z}^{2} \to \mathbb{R}$. In contrast to the reduced version
$C_{red}^{*}(\mathbb{N}^{2})$, we show that the set of KMS states on
$C_{c}^{*}(\mathbb{N}^{2})$ has a rich structure. In particular, we exhibit
uncountably many extremal KMS states of type I, II and III.
