PaginationService.swift

public protocol PaginationServiceType {
    
    associatedtype Element
    
    init(elementProvider: (page: Int, numberOfElements: Int) -> SignalProducer<[Element], NoError>)
    
    func fetchNextPage(numberOfElements: Int) -> SignalProducer<[Element], NoError>
    
}

public final class PaginationService<ElementType>: PaginationServiceType {
    
    public typealias ElementProvider = (page: Int, numberOfElements: Int) -> SignalProducer<[ElementType], NoError>
    
    private let _elementProvider: ElementProvider
    
    private let _currentPage = MutableProperty(0)
    
    public init(elementProvider: ElementProvider) {
        _elementProvider = elementProvider
    }
    
    public func fetchNextPage(numberOfElements: Int) -> SignalProducer<[ElementType], NoError> {
        let updateCurrentPage: [ElementType] -> () = { [unowned self] _ in
            self._currentPage.value = self._currentPage.value + 1
        }
        
        return _elementProvider(page: _currentPage.value, numberOfElements: numberOfElements)
            .on(next: updateCurrentPage)
    }
    
}

ViewController.swift

...

extension ViewController: UITableViewDelegate {
    
    public func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) {
        
        let isLastElement: Bool = { indexPath.row == tableView.numberOfRowsInSection(0) - 1 }()
        
        if isLastElement {
            _viewModel.fetchNewPage().startWithNext { [unowned self] _ in
                self._view.debtsTableView.reloadData()
            }
        }
    }
}

...

ViewModel.swift

public final class DebtsViewModel {
    
    private let _cellViewModels: MutableProperty<[CellViewModel]> = MutableProperty([])

    private let _paginationService: PaginationService<CellModel>
    
    public init(paginationService: PaginationService<CellModel>) {
        _paginationService = paginationService
    }
    
    public func fetchNewPage() -> SignalProducer<(), NoError> {
      let appendNewValues: [CellModel] -> () = { [unowned self] in self._cellViewModels.value.appendContentsOf($0.map(CellViewModel.init)) }
        
      return _paginationService
          .fetchNextPage(10) // Replace with number of elements
          .on(next: appendNewValues)
          .map { _ in () }
    }
    
    public subscript(position: Int) -> DebtViewModel {
      return _cellViewModels.value[position]
    }
    
    public var numberOfItems: Int {
        return _cellViewModels.value.count
    }
}